The Early Clinical Trials Cooperative Group of the EORTC conducted several phase II studies with a pyrimidine analogue of deoxycytidine, 5-aza-2'-deoxycytidine (DAC). The drug was given as three consecutive 1 h i.v. infusions of 75 mg/m2, separated by intervals of 7 h; courses were repeated every 5 weeks. A total of 101 eligible patients were studied: 42 with colo-rectal adenocarcinoma, 27 with squamous cell carcinoma of the head and neck, 18 with malignant melanoma and 14 with renal cell carcinoma. Drug-induced toxicities consisted of moderate myelosuppression, and nausea and vomiting. One single partial remission was seen in a patient with malignant melanoma. DAC given in this dose and schedule is devoid of antitumour activity in adult patients with these refractory types of carcinomas.