Nimodipine was administered at the daily dose of 90 mg po, for 30 days, to ten chronic undifferentiated schizophrenics, eight men and two women, aged 31-35 years, maintained on previously longlasting neuroleptic treatments. In five patients, a placebo period of 15 days preceded the administration of the drug. Monitoring of psychiatric symptomatology by the Brief Psychiatric Rating Scale (BPRS) revealed significant nimodipine-induced improvement. However, the Andreasen Rating Scale for Positive Symptoms (SAPS) showed favourable effects only in the five patients who had not received placebo, while in the others both SAPS and the Andreasen Rating Scale for Negative Symptoms (SANS) showed no significant effect of therapy. The Tardive Dyskinesia Scale revealed no improvements of neurological symptoms after either placebo or drug treatment. Measurement of plasma MHPG concentrations revealed no significant changes induced by either placebo or nimodipine, while HVA plasma levels showed a trend toward decrease, and prolactin a trend toward increase, after nimodipine.