The efficacy and adverse effects of clozapine for patients who cannot be treated with conventional neuroleptics were evaluated by means of a retrospective chart review. The review showed that 85 percent of 503 inpatients experienced slight to nearly complete reduction in symptoms. Adverse effects occurred in 59 percent of patients, although only 7 percent had side effects severe enough to warrant discontinuation of the drug. Data for 70 outpatients treated with clozapine showed that the rate of rehospitalization was significantly lower than before treatment with the drug. These findings agree with those of other European studies and suggest that when hematological and other variables are carefully controlled, the benefits of clozapine therapy outweigh the risks.