Two schedules of cis-dichlorodiammineplatinum(II) (cis-platinum) were evaluated for therapeutic efficacy and toxicity in children with malignant diseases resistant to standard therapy. Initially, cis-platinum was given as a rapid iv bolus injection at a dose of 15 mg/m2/day for 5 days every 3 weeks. The second schedule of cis-platinum was a dose of 1 mg/kg/week administered as an 8-hour infusion with mannitol. furosemide, and hydrating fluids. Using the daily schedule, no responses were seen among 23 children with acute lymphatic leukemia and only eight responses were noted among 47 children with solid tumors. Using the weekly schedule, three responses were noted among 25 children with solid tumors. Responses were observed in seven children with neuroblastoma, two with osteosarcoma, one with embryonal testicular carcinoma, and one with an endodermal sinus tumor. With one exception (a 4-year-old child with neuroblastoma), all responses were of short duration. The most common side effects with both schedules were nausea and vomiting which were usually controlled with antiemetics. The dose-limiting toxicity, especially on the 5-day schedule; was renal function impairment. Only one child who received cis-platinum weekly as an 8-hour infusion with diuresis had elevation of the serum creatinine level. Protocols are being initiated to determine the therapeutic effectiveness and toxicity of combination therapy with cis-platinum in children with neuroblastoma and osteosarcoma.