The role of ABMT in the treatment of acute leukemia patients with poor prognosis is controversial because of the high risk of relapse. We attempted to obtain an anti-tumor effect by administering rIL-2 pre- and/or post-ABMT. We report our experience in 10 consecutive pediatric patients: two AML late responders and eight ALL in 2nd or subsequent CR who received ABMT and rIL-2. Five patients (group A) received rIL-2 only post-ABMT. A 120 h/week rIL-2 'induction' cycle at 6 x 10(6) IU/m2/24 h was administered by continuous intravenous infusion for 2 weeks. A further six maintenance rIL-2 cycles at 18 x 10(6) IU/m2/24 h were given 72 h/week on a monthly basis. Five patients (group B) received a single 120 h cycle of rIL-2 at 6 x 10(6)/m2/24 h before BM harvesting. Three of the five group B patients entered the same protocol described above after ABMT. Increased NK and LAK activity were documented. The cycles were well tolerated; no delayed engraftment in group B was observed. One patient in group A and two patients in group B are still in CCR, respectively 47, 42 and 15 months after ABMT. Our rIL-2 regimen; pre- and/or post-ABMT, was safely tolerated and induced significant immunomodulatory effects in pediatric patients