Clozapine has been shown to be effective in treating schizophrenic patients. In this study we compare the efficacy of clozapine in two groups of treatment resistant psychotics (among the most severe inpatients). 5 chronic schizophrenics (CS). Age 49.6 +/- 12 (paranoid, disorganized residuals). 14 "mixed" patients (MP). Age 34.6 +/- 13, between: major affective disorders (MAD) with mood incongruent psychotic features; schizo affective disorders (SAD). 19 patients (11 females -8 males) have been involved in our trial. They receive 400 up to 800 mg/day of clozapine for a minimum of 12 months and a maximum of 38 months. Treatment responders were defined on the evaluation of the following criteria: scores PANSS-CGI-MADRS (not for the first patients); number of relapses; response to socialisation (exit); quality of life. The results even if based on small sample sizes were classified as: Improvement -->reduction of all major symptoms: patient exit. CS:2/5 (40%); MP:5/14 (35%). Improvement++-->decrease of most major symptoms. CS:1/5 (20%); MP:5/14 (35%). Improvement+-->decrease of one or few major symptoms. CS:2/5 (40%); MP: 1/14 (8%). Failure-->3 from the MP subgroup (16%), 1 leucopenia, 1 worsening, 1 non responder). These finding show that affective disorders and schizoaffective patients are as likely to respond to clozapine as the schizophrenic patients: 60% of the CS and 70% of the MP were very much ( ) and much improved (++). The data also suggest that in the subtype of MP high scores of response occur with the youngest and most recently ill patients (< 30 years, < 18 months).(ABSTRACT TRUNCATED AT 250 WORDS)