We studied Gm typing of serum samples from 838 donors; 177 had chronic hepatitis, 166 liver cirrhosis, 113 primary hepatocellular carcinoma, 21 alcoholic hepatitis, 18 fatty liver and 343 were unrelated normal blood donors. The distribution of Gm phenotypes and haplotypes in sera from patients with primary hepatocellular carcinoma differed from that in the normal controls; the Gm phenotype (1,2,21,13,15,16) and the haplotype Gm1,2,21 were significantly more common in this patient group (X2 = 18.56, corrected P less than 0.01, relative risk = 3.12; X2 = 25.52, corrected P less than 0.005, respectively). Overall, in the other liver diseases, we observed no significant Gm phenotype or haplotype association. The commitment to progression to primary liver carcinoma seems to be ascribable to a gene or polygenes close to the IgG heavy chain loci.