In an attempt to more fully understand the generation of antibody diversity to carbohydrate (CHO) Ag, we produced and characterized a panel of hybridoma cell lines specific for group A streptococcal CHO from mice injected with the intact bacteria (minus the hyaluronic acid capsule and cell wall protein Ag). We have analyzed the use of H and L chain V region genes in the early (day 7) and late response (hyperimmune) and have sequenced the dominant VH gene used in several of our hybridomas. Our data allowed us to assess the extent to which the recombination of various V, D, and J gene segments and somatic mutation contribute to antibody diversification in this system. In this report we confirm that a minimum of two VH and four VK gene segments are used to encode this response. We extend this analysis to show that multiple D and J gene segments are used and that a significant amount of junctional variability is tolerated in CDR 3. Our results indicate that the level of somatic mutation in the hyperimmune response is generally low in comparison with the response to haptens and protein Ag. These data also suggest that there is a positive selection for mutation in CDR 1 during the hyperimmune response to group A streptococcal CHO.