The serum y‐globulin level is a function of the production of immunoglobulins (activity of the lymphoid system) and their catabolism (catab‐olized by the liver). The demonstration of elevated serum y‐globulin is therefore helpful in detection of chronic infections and hepatic or biliary disorders. A semiquantitative test for y‐globulin in canine serum is described. Dilute glutaraldehyde solutions polymerize the most basic serum proteins (γ‐globulins) coagulating the serum. ‘The γ‐globulin test is performed simply by mixing the reagent’ (6 % glutaraldehyde) with serum in the proportion of 1:10. The coagulation time is inversely correlated to the γ‐globulin content in the sera. Hyper γ‐globulinaemic sera will coagulate within 3 minutes.