A rare patient with carbamazepine-induced thrombocytopenia is described. Drug-dependent antibodies of the IgG class were detected and characterized by three different techniques: the clot-retraction inhibition test, the platelet-factor 3 immunoinjury technique, and the serotonin release test. The case illustrates the importance of performing the simple and easily available clot-retraction inhibition test in all the patients with thrombocytopenia associated with drugs.