4'-(9-Acridinylamino)methanesulfon-m-anisidide (AMSA), a derivative of acridine, was evaluated in patients with advanced malignant neoplasms in a phase I clinical trial. The drug was administered in an iv infusion on a weekly x 4 schedule. Seventy-four courses of AMSA were administered to 34 patients over a dose range of 20-90 mg/m2. Dose-limiting toxicity, which was solely hematologic, was observed at 90 mg/m2. Objective antitumor effects were observed in two of 22 evaluable patients: a partial remission in a patient with abdominal desmoid fibrosarcomas and a minor regression in a patient with adenocarcinoma of the colon. A dose of 70-90 mg/m2 would be suitable for trials of AMSA on a weekly basis.