The possible synergism of cisplatin (P) and 5-fluorouracil was studied in 38 consecutive patients with advanced or metastatic colorectal carcinoma. Cisplatin 60 mg/m2 i.v.q. 4 weeks and fluorouracil 600 mg/m2 i.v. weekly were administered for at least 2 cycles, on an out-patient basis, to 24 males and 14 females with a median age of 57 years and a median PS of 80 (Karnofsky). Evaluable lesions were: primary unresectable tumor in 2 patients, local recurrence in 11, liver, lung, bone and soft tissue metastases in 21, 7, 2 and 3 patients respectively. With a median number of 3 cycles administered to 35 evaluable patients, 6 partial responses, 16 unchanged and 13 progressions were observed. Responses were observed in the liver (2 patients), lungs (1) and soft tissues (3). Median remission duration was 15 weeks, median duration of 'unchanged' was 12 weeks. The overall median survival was 24 weeks (30.5 weeks for responders and 22.5 weeks for non-responders). Six patients were pretreated with chemotherapy not containing cisplatin (mainly adjuvant 5-FU). None of them responded. Toxicity was very tolerable with moderate nausea, vomiting and alopecia in the majority of the patients; bone marrow toxicity was generally mild with no blood transfusions required, no complications of myelosuppression (sepsis or bleeding) and no chemotherapy-related deaths. In this experience the combination of low dose cisplatin with fluorouracil, does not appear to significantly enhance 5-FU toxicity and the response rate is not superior to that reported with 5-FU alone. However, better designed schedule combinations with optimal doses, sequences and exposure time of the 2-drug regimen, seem necessary to obtain the biochemical events that support the potentiation.