To the Editor.—Ìý Clozapine has been shown to be superior to chlorpromazine and haloperidol in treatment-resistant schizophrenic patients.¹ It has not yet been approved for use in the United States, but it is available in over 100 sites on a compassionate need basis. Well over 500 patients are currently receiving it in this country. The duration of an adequate trial is, therefore, of critical importance. In the study by Kane et al,¹ only 30% of patients had responded within 6 weeks of starting drug therapy. Other studies or commentaries on the use of clozapine in treatment-resistant patients have not addressed this issue.^2-5We have now administered clozapine on an open basis to 51 schizophrenic patients who are comparable to the group studied by Kane et al.^1,6 Sixteen (31.4%) of the 51 patients responded within 6 weeks with a 20% or more decrease in the