The spectrum of therapeutic and adverse effects of zotepine and their relationships with serum concentrations of the drug were investigated in 28 schizophrenic inpatients by a fixed-dose (100 mg/day for the first 1 wk and 200 mg/day for the following 3 wk) study. The mean % improvement in Brief Psychiatric Rating Scale (BPRS) scores were 63.4% for total, 64.4% for positive, 41.8% for negative and 74.2% for anxiety-depression symptoms, suggesting that zotepine has a broad therapeutic spectrum. There were significant differences in improvement of negative symptoms after 1 wk and total and positive symptoms after 2 wk (P < 0.05) between responders (more than 50% reduction in total BPRS scores at wk 4) and nonresponders. The mean scores of UKU Side Effect Rating Scale were low in this study. UKU scores of psychic at wk 2 and total adverse effects at wk 3 and wk 4 (P < 0.05) were higher in nonresponders than in responders. A negative correlation between % improvement in total BPRS and total UKU scores was observed (P < 0.05). These two results suggest some relationship between poor clinical response and increased adverse effects during zotepine treatment. Lack of close correlation between serum drug concentrations and clinical or adverse effects indicates that therapeutic monitoring of zotepine concentrations would be of little significance.