Serum IgG subclass levels were assessed by ELISA in 30 week old SHR-A3, SHR-B2 and SHR-A3(IgH SHR-B2), n = 6 per group. Significant differences in IgG1, IgG2b and IgG2c in SHR-A3 versus SHR-B2 were observed. In the congenic line, transfer of the SHR-B2 IgH segment into SHR-A3 resulted in serum IgG subclass levels that closely resembled the donor (SHR-B2) levels for IgG2b and IgG2c. For IgG2a, no effect of congenic transfer was predicted based on prior mapping, though a reduction was observed in the congenic line. For IgG1, the congenic levels were intermediate between the donor and recipient levels and not significantly different from either (*** p<0.001, ** p<0.01, *, p<0.05, NS not significantly different).