The direct antiglobulin consumption (DAC) test, used for the detection of platelet autoantibodies, was found to be positive in 86% of a group of 150 patients with thrombocytopenic purpura. The platelet radioactive Coombs’ (DRC) test was performed in 30 patients and the correlation between the two tests was statistically significant (r = 0.48, p < 0.01). The two tests were used in an indirect mode for the detection of antiplatelet antibodies in serum. The results of the two tests were in good agreement (r = 0.66, p < 0.001). There was not a statistically significant correlation between the level of platelet-associated IgG and the presence of platelet antibodies in the serum. These results indicate that the DAC test or DRC test can be used interchangeably for the detection of antibody in serum or of antibody bound to platelets, and that only the direct test, using the patients’ platelets, is useful in the diagnosis of autoimmune thrombocytopenic purpura.