An immune adherence hemagglutination (IAHA) test has been developed for the rapid detection of antibodies againstToxoplasma gondii. This test, which utilizes human type 0 erythrocytes andToxoplasmaorganisms fixed in formaldehyde solution, is easy to perform, safe, and sensitive. Like theToxoplasmadye test, the IAHA reaction detects antibodies to surface antigens ofToxoplasma. Unlike theToxoplasmadye test, the procedure does not require the continuous maintenance of living parasites. Sera from 80 patients presumed to have toxoplasmic retinochoroiditis and from two rabbits with establishedToxoplasmainfections were tested by the dye test, the standard hemagglutination (HA) test, and the IAHA test. While there was good general agreement of results in all three tests, the results of the IAHA test correlated more closely with those of the dye test than with those of the standard HA test.