Abstract: A quanitiative method for measuring IgM, IgG and total hemolysin in serum is described. Immune mice serum (nontreated for determing IgM or treated with equal volume of 2-mercaptoethanol 0.2 mol/L for IgG). Sheep red blood cells (SRBC), guinea pig complement and-where applicable-sheep antimice immunoglobulin G serum were incubated at 37℃ for lh in fluid phase, centrifuged, and the supernatant read at 540 nm. Hemolysin concentration was calculated by OD₅₄₀×dilution of serum.The IgG, IgM and total hemolysin concentrations in mice treated with hydrocortisone, cyclophosphamide or antilymphocyte serum (ALS) were decreased, but those of Bacille Calmette-Guerin (BCG) or levamisole treated mice were increased.It seems that this method is simple, rapid and exact.