A phase I trial with continuous intravenous infusion of lobaplatin (D-19466; 1,2-diamminomethyl-cyclobutaneplatinum (ll)-lactate) for 72 h was performed to determine the maximum tolerated dose (MTD). Each patient received a single dose level, the total dose of lobaplatin ranged from 30 to 60 mg/m2/72 h every 4 weeks. Eleven patients enroled in this study and received a total of 30 courses of lobaplatin (median 2; range 1–6). Thrombocytopenia was the dose-limiting toxicity, it reached WHO grade III in three out of six patients at 45 mg/m2/72 h, and WHO grade IV in two out of two patients at 60 mg/m2/72 h. Leucocytopenia was mild, as was nausea and vomiting. Phlebitis at the infusion site was found in three patients. During this trial there were no signs of renal, neuro- or ototoxicity. One patient with ovarian cancer, pretreated with three different platinum complexes, achieved a partial response now lasting for longer than 6 months. In conclusion, thrombocytopenia is the dose-limiting toxicity of lobaplatin administered by 72 h continuous infusion. The recommended phase II dose for this regimen is 45 mg/m2/72 h every 4 weeks.