L chains derived from anti-group A streptococcal carbohydrate antibodies raised in A/J, BALB/cJ, C57BL/6J, CB-20, BAB-14, and CAL-20 mice were examined by isoelectric focusing. Multiple strain-associated differences in the degree and frequency of expression of particular L chain spectrotypes were observed. Analysis of L chain-focusing patterns in allotype-congenic mice revealed that IgCH-linked genes can have profound effects on the L chain phenotypes expressed by strains with identical L chain genotypes. Lastly, the overall spectrotypic diversity of L chains from anti-GAC antibodies appears to be less extensive than the diversity of the antibodies from which these L chains derive, documented by similar techniques. These results are interpreted in light of the significance of combinatorial diversity in generating antibody heterogeneity.