Background. Docetaxel and irinotecan have additive or synergistic activity in vitro and in vivo as well as differing toxicities and unique mechanisms of action. We conducted a phase I trial to determine the maximum-tolerated dose of docetaxel and irinotecan given on a weekly schedule. Methods. Eligible patients had advanced, incurable, solid tumors. Docetaxel was administered as a 1-hour infusion and escalated over four dose levels (25, 30, 35, and 40 mg/m(2)) followed by irinotecan administered over 30 minutes at a fixed dose of 50 mg/m(2). Treatment was administered weekly for four weeks followed by two weeks of rest. To improve tolerability, the schedule was modified to weekly administration for two weeks with one week of rest, and irinotecan was escalated over 3 dose levels (55, 60, and 65 mg/m(2)) with docetaxel fixed at 35 mg/m(2). Results. Forty-four patients were treated and the most common dose-limiting toxicity was diarrhea observed in 11% of patients. Severe neutropenia was rare (grade 4: 2%, grade 3: 23%). Other nonhematologic toxicities included nausea/vomiting, dehydration and fatigue. Partial responses occurred in two patients with pancreatic cancer, and one patient each with non-small cell lung and esophageal cancer. Conclusions. Weekly docetaxel and irinotecan is a promising non-cisplatin doublet with preliminary evidence of activity in advanced solid tumors. Diarrhea is the predominant dose-limiting toxicity but unlike the every 3 weeks schedule myelosuppression is modest. The recommended phase II doses are docetaxel 35 mg/m(2) and irinotecan 60 mg/m(2) on days 1 and 8 of a 21-day schedule. Phase II trials of this regimen are ongoing or planned in lung, head and neck, stomach, esophageal, and pancreatic cancers.