3H-spiroperidol binding to peripheral blood mononuclear cells was measured in 28 patients, who fulfilled DSM-III-R-criteria for schizophrenia and 17 healthy subjects. There were no significant differences in characteristic binding parameters (Kd, Bmax) between schizophrenic and healthy subjects. Moreover, there was no relation of binding parameters to any of the subtypes of schizophrenia or to the course of illness according to DSM-III-R-criteria. However, some patients exhibited higher Bmax values without having a unique clinical symptomatology according to known diagnostic criteria. Neuroleptic treatment had no consistent effect on binding parameters intraindividually. Kd and Bmax values were not related to age or gender. In conclusion, despite our previously reported improved methodology, we were not able to corroborate the clinical importance of this "peripheral marker" as a tool for diagnosing schizophrenia or for predicting the response to neuroleptic treatment in our sample of schizophrenic patients.