Growth and carcass traits are economically important traits of beef cattle and are under the control of multiple genes. Genetic markers for these candidate genes may be useful in marker-assisted selection. Three genes, Pit-1, growth hormone releasing hormone receptor (GHRH-R), and insulin-like growth factor II (IGF-II), were analyzed in this study. Pit-1 is a pituitary specific transcription factor and is able to positively regulate the expression of growth hormone, prolactin, and thyrotrophin b subunit. GHRH-R is the receptor for growth hormone releasing hormone, which stimulates the secretion of growth hormone (GH) and regulates mammalian linear growth through its receptor. IGF-II has been shown to regulate pre-adolescent growth. Therefore, these three genes all influence growth and are important candidate genes. The experimental animals used in this study were Angus beef cattle, which were divergently selected for high or low blood serum insulin-like growth factor I (IGF-I) concentration. DNA was extracted from blood samples and the target DNA segments were amplified by PCR. Primers were designed based on DNA or mRNA sequences in Genbank. When amplification was achieved, SSCP (single strand conformation polymorphism) analysis was used to screen for mutations within the amplified segment. After an SSCP polymorphism was found, the PCR product of the two homozygous segments was sent for sequencing in order to determine the nature of the detected polymorphism. Proper restriction enzymes were determined for the polymorphisms based on the DNA sequence and used to facilitate genotyping using PCR-RFLP (restriction fragment length polymorphism). Associations of the animal genotypes for each polymorphism with growth and carcass traits were analyzed using General Linear Model (GLM) procedures in the Statistical Analysis System (SAS). Three polymorphisms, Pit1I3H (HinfI), Pit1I3NL (NlaIII), and Pit1I3N (NciI), were detected in intron 3 of the Pit-1 gene. One polymorphism, Pit1I4N (BstNI), was found in intron 4 and one single nucleotide polymorphism (SNP) (Pit1I5) was found in intron 5. For the Pit1I3H polymorphism, genotypes CC, CD, and DD were detected with frequencies of .12, .49, and .39, respectively; there was an AAT deletion in allele C. For the Pit1I3NL polymorphism, genotypic frequencies of .12, .47, and .41 were observed for GG, GH, and HH genotypes, respectively; a G to C transition in allele G was observed. The Pit1I3N polymorphism was found to have genotypes MM, MN, and NN with frequencies of .12, .51, and .37, respectively. For the Pit1I4N polymorphism in intron 4, genotypes EE, EF, and FF were detected and had frequencies of .12, .47, and .41, respectively; a G to T transition was found in allele E. The previously reported polymorphism in exon 6, Pit1E6H (HinfI), was also studied and the frequencies of genotypes OO, OP, and PP were .11, .44, and .45, respectively. The intron 5 SNP, Pit1I5, was found to have genotypes AB and BB with frequencies of .09 and .91, respectively. No AA individuals were found. The A allele had a single nucleotide transition from G to T. No significant associations with growth or carcass traits were observed for Pit1I3H, Pit1I3NL, Pit1I3N, Pit1I4N, or Pit1I5. For Pit1E6H, a significant relationship was found with birth weight (P= .03), where genotype OO had the lowest mean. However, genotype OO was found to be superior for preweaning gain (P= .01) and weight gain during the 20-d period between weaning and the beginning of the postweaning test (P= .06). Significant effects of the Pit1E6H genotypes were observed on backfat thickness (P= .01) in the high IGF-I line, and on marbling score (P= .03) in the low line. One polymorphism, GHRHRE6N (NciI), was detected in exon 6 of the GHRH-R gene of Angus cattle. Genotypes AA, AB, and BB were observed with frequencies of .80, .19, and .01, respectively. Allele B has a point mutation from A to G in codon 189, which results in an amino acid change from Glutamine to Arginine. No significant associations of the genotypes with growth, carcass traits, or IGF-I concentrations were observed for this polymorphism. Another polymorphism was detected in the promoter region of the GHRH-R gene of Jersey cattle. Genotypes AA, AB, and BB were observed with frequencies of .44, .53, and .03, respectively. This polymorphism was due to a C to T mutation in allele B. Restriction enzyme AciI was used to genotype this SNP. Significant relationships were observed between genotypes of this polymorphism and relative value of milk production (P= .05) in Jersey cows. Animals with genotype AB tended to have the highest mean for this trait. Therefore, it is assumed that this polymorphism had an overdominant effect on milk production. An AciI polymorphism was observed in intron 8 of the IGF-II gene. Two alleles, A and B, and three genotypes, AA, AB, and BB, were observed. Genotypic frequencies of AA, AB, and BB were .15, .43, and .42, respectively. Sequencing results demonstrated a transition from T to G in allele A. Restriction enzyme AciI was used to genotype this SNP. Significant associations were found between genotypes and weight gain during the 20-d period between weaning and the beginning of the postweaning test (P= .05) and IGF-I concentration at d 28 of the 140-d postweaning test (P= .02). In addition, moderate relationships of the genotypes with preweaning gain, on-test weight, off-test weight, and weight at d 28 and 56 of the 140 postweaning test were observed. For all of these traits, genotype AB had a significantly higher mean than genotype AA. Significant relationships were also observed for ribeye area (P= .01) and yield grade (P= .03). Animals with AB genotype had the highest mean for ribeye area, whereas BB animals had the highest yield grades. In conclusion, the polymorphism Pit1E6H in the Pit-1 gene may be a useful marker for preweaning growth rate. Genotype OO was associated with lower birth weight and higher preweaning weight gain. The AciI polymorphism observed in the IGF-II gene may have a dominant effect on growth traits; the B allele was the favorable allele for growth rate. For carcass traits, genotype AB was the favorable genotype for both ribeye area and yield grade.