An inhibition enzyme-linked immunosorbent assay (inhibition-ELISA) was developed for the quantitative determination of human IgG (Gm) allotypes using rabbit anti-Gm antisera, alkaline-phosphatase-conjugated goat anti-rabbit IgG and, as the calibrant, purified human myeloma proteins possessing the relevant Gm allotype. The assay is reproducible and can detect as little as 10 ng/ml of G1m(a), G2m(n) or G3m(st), and 100 ng/ml of G1m(f) or G3m(g). Using this assay, the "gene dosage effect" and "allelic balance" in healthy Japanese were studied.