Thrombocytopenia associated with gold therapy is thought to be due to an immune-mediated mechanism. Relatively few patients have been studied so far, and precise details of the pathophysiology of this disease remain undetermined. We report a patient with gold-induced thrombocytopenia resulting from auranofin therapy. The patient's plasma contained platelet-reactive antibodies detectable only in the presence of gold salts. Antibody binding occurred at gold concentrations ranging from 0.01 to 10,000 ng/ml. The binding occurred independently of gold salt used, suggesting that substitution of a different gold preparation in this patient would result in a similar thrombocytopenia. These data support a drug-dependent immune mechanism for platelet destruction.