CI-921, a 4,5-disubstituted analog of amsacrine, has been selected for clinical testing because of its experimental activity in vitro and in vivo against solid tumors as well as leukemias. In studies conducted by Baguley and co-workers, CI-921 demonstrated activity against Lewis lung carcinoma in vivo, producing marked increases in life span and a high proportion of 60-day survivors. An intermittent schedule of administration was more effective than a daily X 5 or daily X 9 schedule. In pharmacokinetic studies in dogs, CI-921 achieved higher plasma concentrations and was cleared more slowly than amsacrine. CI-921 is readily soluble in water and may have antitumor activity when administered orally. Animal toxicology studies indicate that dose-related, reversible leukopenia and thrombocytopenia occur, as well as gastrointestinal toxicity, elevation of alkaline phosphatase and generalized lymphoid depletion. Phase I clinical testing of a parenteral formulation is in progress.