Plasma cells (PCs) are one of the two major cell types generated during germinal center reactions. To test the hypothesis that PCs express a unique repertoire of immunoglobulin (Ig) genes resulting from intensive antigenic stimulation and selection, the mutational pattern and distribution of V_H gene segments within 178 transcripts amplified from individual IgM and IgA secreting tonsil PCs were analyzed. The results demonstrated that both μ and α transcripts expressed repertoires with limited diversity. Moreover, both μ and α transcripts were heavily mutated, with a significantly increased mutational frequency noted for α compared to μ transcripts (5.0×10⁻² vs 1.8×10⁻², P<0.001). In addition, both μ and α transcripts showed significantly greater targeting of mutations to RGYW motifs (purine/guanine/pyrimidine/A or T) compared to memory B cells. Finally, clonally expanded cells were detected in α but not μ PC compartments. These results indicate that antigen driven stimulation and selection shape the entire expressed PC repertoire, but the impact is greater in α expressing PCs.