1. There is an ongoing controversy, if increased binding of 3H-spiperone to lymphocytes might discriminate between schizophrenia and other psychiatric diseases or even be a genetic vulnerability marker for schizophrenia, or predict the response to neuroleptic treatment. 2. Some critical methodological details which might contribute to this controversy are described. 3. 3H-spiperone binding was evaluated in 31 patients with schizophrenia, 7 patients with schizoaffective disorder, bipolar type, 6 patients with a manic episode and 6 patients with a depressive episode of bipolar major affective disorder (DSM-III-R criteria), and in 19 healthy subjects. 4. There were no significant differences in characteristic binding parameters (KD, Bmax) between all groups of psychiatric in-patients and in comparison to healthy subjects. Moreover, there was no relation of binding parameters to any of the subtypes of schizopherenia or to the course of illness according to DSM-III-R-criteria. 5. Neuroleptic treatment or clinical response to treatment had no consistent effect on binding parameters intra-individually. 6. In summary, 3H-spiperone binding to lymphocytes failed to differentiate between the diagnostic subgroups (DSM-III-R) and between treatment responders and non-responders in our sample of patients.