The activity of cisplatin against advanced metastatic adenocarcinoma of unknown primary site (ACUP) was evaluated in 21 patients. Cisplatin (100 mg/m2) was given as a 4-h continuous infusion every 3 weeks, with appropriate fluids and diuretics. The overall response rate was 19% with 1 complete remission for 12 months and 3 partial remissions lasting from 4 to 7 months. 7 patients achieved stable disease and in 9 patients the disease was progressive. The median duration of response was 6.5 months. The median survival 7.5 months. The median survival of the total patient group was 5 months (range 1-18 months). Toxicity comprised mainly nausea and vomiting, mild creatinine elevation and leukocytopenia. Slight ototoxicity was observed in 6 patients.