In this work, we provide new analytical and computer simulation results for the performance of multitone (MT) DS-SS signaling in the presence of narrowband and partialband interference. We look at two transformations on the input data, serial to parallel conversion and replication. We investigate the tradeoff between the number of subcarriers and the per-subcarrier processing gain, for a fixed data rate and fixed bandwidth, and also compare with the conventional single-carrier (SC) system. Our results show that in the presence of single and multiple tone interference, MT DS-SS and conventional SC system have similar performance.