Paclitaxel represents a novel antitumour agent with demonstrated activity in cisplatin-sensitive tumours, particularly ovarian cancer. In addition, responses to paclitaxel have been observed in patients with cisplatin-refractory ovarian cancer. The role of paclitaxel in the treatment of testicular cancer has not been explored so far. Despite the generally high cure rates in patients with metastatic testicular cancer, patients with relapsed disease not responding to platin-based salvage chemotherapy have an extremely poor prognosis. In a phase I/II trial 10 patients with relapsed, cisplatin-refractory malignant germ-cell tumours were treated with paclitaxel as 6-h infusions (8 patients) or 3-h infusions (2 patients) at doses from 135 mg/m2 to 310 mg/m2 at 3-week intervals. Three patients achieved a response to paclitaxel, but disease recurred shortly in two patients after two and four cycles of therapy, respectively. One patient has remained in marker-negative partial response for more than 5 months. The toxicity of paclitaxel was tolerable for a dose range from 135 mg/m2 to 225 mg/m2. Granulocytopenia, WHO grades 3 and 4, occurred in all patients but was of short duration (median 3 days; range: 2-7 days). Other toxicities such as mucositis (5 patients grade 1), neurotoxicity (1 patient grade 1, 2 patients grade 2), infection (1 patient grade 3) and diarrhoea (1 patient grade 2) were not dose-limiting. There were no hypersensitivity reactions, but 1 patient developed severe myalgias during therapy with paclitaxel. Six patients with documented cisplatin-refractory disease were retreated with cisplatin-based chemotherapy after paclitaxel treatment and, in 4 of these, tumour responses of 3, 4, 5 and more than 5 months duration were achieved. In order to explore the role of paclitaxel in relapsed and/or cisplatin-refractory testicular cancer a phase II study using a 3-h infusion of 225 mg/m2 paclitaxel every 3 weeks, conducted by the German Testicular Cancer Study Group, is ongoing.