A phase II study utilizing 5-azacytidine in the treatment of patients with solid tumors was carried out by the Southwest Oncology Group (SWOG-7208). Of 214 patients entered in the study 191 were eligible and 167 were evaluable. While initially they received 225 mg/m2 iv on Days 1--5 every 3 weeks because of toxicity the dose was subsequently reduced to 175mg/m2 and later to 150 mg/m2. Five partial regressions, 2.6% of the eligible patients and 3% of the evaluable patients, lasting from 28 to 77 days were observed. Sixteen patients 8.4% of the eligible patients and 9.6% of the evaluable patients, had no significant change in their disease for 39--255 days. The major toxicities were myelosuppressive and gastrointestinal with 13 deaths attributable to drug toxicity: 11 due to sepsis and two due to cerebral hemorrhage. 5-Azacytidine induced few favorable responses; those that did occur usually were of poor quality and short duration and were associated with significant toxicity.