The levels of mink C gamma-allotypes (H3, H4, H6 and H8) were determined in sera, and the proportion of the corresponding allotype-synthesizing B cells was estimated in peripheral blood, spleen and mesenteric lymph nodes. Individual differences in H6 levels and, possibly, those in H8 were entirely dependent on the proliferation degree of the corresponding clone of B cells and also determined by the dosage of the structural gene. There was no correspondence between the great numbers of H3+, H4+ cells and low levels of H3 and H4 allotypes in the sera of the majority of minks with their minor expression. A possible cause of this discrepancy may be a blockade of the secretion of IgG by H3+, H4+ cells. There exists most likely a gene (or genes) controlling the blockade of IgG secretion. The regulation of C gamma-allotype expression is presumably effected in a manner specific to each of the allotypes.