ICRF-187 (NSC-169780), the (+) enantiomer of the racemic antineoplastic agent ICRF-159 (NSc-129943), was administered intravenously for five days every three weeks to 18 patients in a phase I study. Leukopenia was the dose-limiting toxicity. Mild reversible elevations in SGOT and bilirubin were common. Other toxicities were mild and infrequent. Recommended doses of ICRF-187 for phase II studies are 800 mg/m2 for heavily pretreated patients and 1250 mg/m2 for patients with little or no prior therapy. A daily five day intravenous schedule should be used. Other potential clinical uses of ICRF-187 are discussed.