The Phase I study of N-7-(p-hydroxyphenyl)-mitomycin C (KW 2083, M 83) was performed. The dose-limiting toxicity was leukopenia and thrombocytopenia and a maximum tolerable dose was 70 mg/m2. Nonhematologic toxicities included nausea (44%), vomiting (13%), diarrhea (2.7%), azotemia (8.1%), proteinuria (5.4%), alopecia (8.1%) and elevated hepatic enzymes (2.7%). This Phase I study indicates that the recommended starting dose for Phase II studies for patients without significant myelosuppression would be 50 mg/m2 at 6 week intervals in an intravenous push. KW 2083 should be avoided in patients with impaired renal functions and proteinuria because of permanent renal damages caused by the drug.