We report the outcome of 50 consecutive patients with CR1 acute leukemia (AML = 22; ALL = 28) treated with autologous BMT, after cyclophosphamide and TBI, followed with a sequential high dose rIL2 regimen. rIL-2 (RU 49637 from Roussel-Uclaf, Romainville, France) was started after hematological reconstitution an average of 72 +/- 22 days post transplant. The schedule consisted of a continuous infusion over 5 cycles (Cycle 1: 5 days starting on day 1; cycle 2-5: 2 days starting on day 15, 29, 43 and 57). Patients were treated at 4 different dosages (12 (N = 40), 16 (N = 3), 20 (N = 2), 24 (N = 5) x 10(6) IU/m2/day). Toxicities were mainly related to capillary leak syndrome and thrombocytopenia. Patients received an average of 122 +/- 49 10(6) IU/m2. Two patients with AML died from toxicity. rIL-2 infusion was associated with very a high level of immune stimu-lation of both T-cells (P < 0.05) and natural killer (NK) cells (P < 0.05) and associated cytolytic functions (P < 0.05). With a minimal and median follow-up of 21 and 46 months, 3 year leukemia free survival is 41 +/- 6% overall, 39 +/- 10% and 43 +/- 8% for AML and ALL respectively. Relapse probabilities at 3 years are 59 +/- 11% for AML and 57 +/- 8% for ALL. We conclude that this short infusion of rIL-2 over 2 months, resulting in an increased immune stimulation, is not associated with a better leukemic control for patients with acute leukemia transplanted early after reaching first complete remission.