The purpose of this study was to determine the safety of irinotecan and capecitabine in patients with advanced solid tumors. Thirty-four patients received 122 courses of irinotecan 200 to 300 mg/m(2) as an intravenous infusion during 30 minutes on day 1 and capecitabine 1,500 to 3,000 mg/d orally 12 hours apart starting on day 2 for 14 days, repeated every 21 days (one course). Three to seven patients were treated in six dose-escalation cohorts. Three of 7 (43%) patients treated with irinotecan 300 mg/m(2) and capecitabine 2,300 mg/d had course 1 dose-limiting toxicity (DLT) defining maximum tolerated dosage (MTD). Fatigue and diarrhea were the major DLTs, and other events included neutropenia, anorexia, and hand-foot syndrome. At one dose level below the MTD, none of 7 patients treated with irinotecan 275 mg/m(2), and capecitabine 2,300 mg/d (36 courses) had course 1 DLT. Grade III to IV toxicities beyond course 1 included neutropenia (11% of all courses), fatigue (3.4%) and hand-foot syndrome (3.4%). There were only two episodes of febrile grade II neutropenia. There were no toxic deaths. Transient antitumor response was noted in one patient with irinotecan and 5-fluorouracil-refractory colon cancer. The combination of irinotecan 275 mg/m(2) and capecitabine 2,300 mg/d represents a safe, favorable, and convenient outpatient regimen warranting further phase II evaluation.