The prevalence of immunologic and coagulation disorders in 75 schizophrenic patients treated with chlorpromazine or other antipsychotic drugs was evaluated. Four groups were studied: Group A, chlorpromazine treatment for more than 2 1/2 years; Group B, chlorpromazine and other antipsychotic drug treatment for more than 2 1/2 years; Group C, chlorpromazine treatment for less than 2 1/2 years; Group D, no chlorpromazine, but other antipsychotic drug treatment. Significant elevation of serum IgM and prolongation of partial thromboplastin time were noted in patients who had long-term chlorpromazine treatment. The latter was caused by a circulating inhibitor resembling that seen with systemic lupus erythematosus. There was a significant correlation between the IgM level versus chlorpromazine dose or duration of treatment and the partial thromboplastin time versus chlorpromazine dose or duration of treatment. In Groups A and B, 63% had a positive antinuclear antibody test (greater than or equal to 1:80), 40% had antibodies to native DNA, and 58% had antibodies to nucleoprotein. These antibodies were negative in the other groups. The percentages of T lymphocytes were below normal in 13 of 41 patients treated with chlopromazine. Twenty of 42 patients in Groups A and B, and none of 28 in Groups C and D had splenomegaly. This study indicates that most patients on long-term chlorpromazine treatment develop one or more immunologic abnormalities.