A phase I trial was conducted with recombinant human interleukin-1 beta (rhIL-1 beta) in patients undergoing autologous bone marrow (BM) transplantation for acute myelogenous leukemia. rhIL-1 beta was administered at 3 dose levels (0.01, 0.02, 0.05 microgram/kg) by 30 minute intravenous infusion once a day beginning on the day of BM infusion and continuing for a total of 5 doses. A total of 17 patients were entered on the trial, and their results were compared with those of 74 consecutive historical control patients that did not receive colony stimulating factors. Moderate toxicity was observed in all patients. All 17 patients developed fever and chills within 30 minutes after initiation of rhIL-1 beta, and hypotension was observed in 14 of 17 patients 5 to 8 hours after the infusion. A total of 30% of patients required therapy (normal saline or dopamine) for treatment of hypotension. Therefore, dose escalation was discontinued at the 0.05 microgram/kg dose level. The number of days required to achieve an absolute neutrophil count greater than 500 mL in patients who received rhIL-1 beta was less than in historical patients (25 v 34; P = .02). This appeared to correlate with a reduced incidence of infection between days 0 and 28 after BM infusion (12% v 23%; P = .049). Median bilirubin, median creatinine, platelet recovery, and days in the hospital were not different between study patients and historical controls. Survival of patients who received rhIL-1 beta compared with that of historical patients was improved (30% v 20%; P = .04). These possible benefits were achieved at the cost of moderate toxicity during rhIL-1 beta administration.