The compound 4''-(9-acridinylamino)methanesulfon-m-anisidide [an antineoplastic drug] is a new acridine derivative that was evaluated in a Phase 1 clinical trial. The schedule of drug administration consisted of daily i.v. injection for 3 consecutive days, repeated at 3 wk intervals. Patients (26) received 63 courses of 4''-(9-acridinylamino)methanesulfon-m-anisidide in a dose range from 4-50 mg/m2 per day. Hematopoietic toxicity was dose limiting, but it was of short duration and rapidly reversible. Mild nausea and vomiting were observed in 16% of the courses, and a mild degree of phlebitis was observed in 10% of the courses. Responses were observed in 2 patients with adenocarcinoma of the lung and 1 each of melanoma and acute myeloblastic leukemia. Phase 2 studies of 4''-(9-acridinylamino)methanesulfon-m-anisidide are planned at a starting dose of 40 mg/m2 per day for 3 days in good-risk patients and at 25-30 mg/m2 per day for 3 days in poor-risk patients. Course of treatment would be repeated at 21 day intervals.