Docetaxel is a widely active cytotoxic agent. The principal dose-limiting toxicities (DLTs) of the 3-weekly regimen are neutropenia and febrile neutropenia. Use of prophylactic granulocyte colony-stimulating factor (G-CSF) may allow higher doses of docetaxel to be administered with potentially greater anticancer efficacy. The objectives of this study were to determine the maximum tolerated dose (MTD) and toxicity profile of docetaxel given with G-CSF support.Eligible patients had solid tumours and were aged 18-75 years with a WHO performance status of up to 2. Strict criteria for liver function were followed. Patients may have received one previous regimen of chemotherapy in addition to adjuvant chemotherapy. Cohorts of three to six patients received docetaxel over 60-90 min every 3 weeks, commencing at 110 mg/m(2) and escalating at 10 mg/m(2) increments. Patients also received G-CSF 5 micro g/kg/day until neutrophil recovery. A 3-day corticosteroid prophylaxis was given.Twenty-nine patients with median age 55 years (range 29-75) were included. Fourteen (48%) had previously received chemotherapy. At the 170 mg/m(2) dose level (the MTD), two of three patients had DLTs and 160 mg/m(2) was determined to be the recommended dose. The principal DLTs were skin and neurosensory toxicity. Asthenia was frequent, especially at dose levels >/=140 mg/m(2). Grade 4 neutropenia occurred in only 10 patients (35%) and was not dose related, with febrile neutropenia in three patients (10%).Docetaxel may be escalated considerably above standard doses when administered with G-CSF support. The recommended dose for phase II studies is 160 mg/m(2). With escalated-dose docetaxel, DLTs were non-haematological and qualitatively similar to the toxicity profile at standard doses.