The purpose of this study was to determine the dose-limiting toxicities and the maximum-tolerated dose (MTD) of weekly administration of paclitaxel in patients with advanced solid tumors. Twenty-six patients with advanced solid tumors were treated with escalated doses of paclitaxel (starting dose 70 mg/m(2)/wk with increments of 10 mg/m(2)/wk) for 4 consecutive weeks every 6 weeks. No intrapatient escalation or growth factor support was allowed. The DLT was exceeded at the dose of 120 mg/m(2)/wk, and the dose-limiting events were grade IV neutropenia and treatment delay because of incomplete hematologic recovery. There was no cumulative myelosuppression. Grade IV neutropenia occurred in four (6%) cycles, and there was one episode of febrile neutropenia. Grade II/III fatigue occurred in 19 (73%) patients, resulting in discontinuation of treatment in 2 of them; grade II neurosensory toxicity and grade II alopecia occurred in 8 (31%) patients each. The MTD, which is also the recommended dose for further phase II studies, was 110 mg/m(2)/wk. Among the 21 patients with bidimensionally measurable disease, 2 (10%) partial responses were observed, both in patients with heavily pretreated advanced breast cancer. The weekly administration of paclitaxel for 4 consecutive weeks in cycles of 6 weeks is a feasible, safe, and active outpatient regimen that merits further evaluation in combination with other anticancer agents.