A single-agent dose-escalating phase I study on the novel sulfonamide E7070 was performed to determine the toxicity profile and the recommended dose for phase II studies. The pharmacokinetic profile of E7070 was also determined. E7070 was administered as a continuous infusion over 5 days repeated every 3 weeks. 27 patients were treated at doses ranging from 6 to 200 mg/m(2)/day. As with other administration schedules, the dose-limiting toxicities were dose-dependent, reversible neutropenia and thrombocytopenia. Although no objective responses were observed, seven patients had stable disease. E7070 displayed a non-linear pharmacokinetic profile, especially at dose-levels greater than 24 mg/m(2)/day, with a reduction in clearance and an increase in the half-life at the higher dose levels. The risk of myelosuppression became significant with an AUC greater than 4000 microg h/ml. The recommended dose of E7070 for further studies is 96 mg/m(2)/day when administered on a 5-day continuous infusion schedule every 3 weeks.