SUMMARYComparisons were made of the specificity and sensitivity of chromium release cytotoxicity, cytotoxicity as determined by dye uptake, and colony inhibition (CI) techniques for detecting membrane-associated alloantigens on cultured human and chimpanzee fibroblasts. All three techniques gave similar results and demonstrated allospecificities. Although the specificities detected by each of the methods were similar, certain distinctive features which might influence selection of one method over the other are discussed.