Sera from patients with a clinical diagnosis of halothane hepatitis have been shown to contain antibodies that react with liver microsomal proteins (100, 76, 59, 57, and 54 kDa) covalently altered by the trifluoroacetyl (TFA) halide metabolite of halothane. In the present study, rapid and sensitive enzyme-linked immunosorbent assays for the detection of these antibodies have been evaluated. A recently described method that utilizes TFA-rabbit serum albumin as test antigen was studied employing a large population of halothane hepatitis and control patients. Several problems were discovered with the assay that were not previously recognized. The assay was then compared directly with methods that utilize as test antigens either liver microsomes or purified TFA proteins from halothane-treated rats. Sixty-seven percent of patients with a clinical diagnosis of halothane hepatitis tested positive for antibodies when the test antigens were either TFA-rabbit serum albumin or liver microsomes. This value was increased to 79% when the purified TFA-57 kDa, TFA-76 kDa, and TFA-100 kDa proteins were used as test antigens. These results indicate that the specificity and sensitivity of enzyme-linked immunosorbent assay methods for the detection of patients' antibodies may be increased significantly by utilizing the purified TFA microsomal proteins as test antigens.