We evaluated the efficacy of recombinant human interleukin-3 (rhIL-3) in reducing the number of platelet transfusions and major infections after autologous bone marrow transplantation (ABMT) in patients with malignant lymphoma. 198 patients with non-Hodgkin's lymphoma (NHL, n = 111) and Hodgkin's disease (HD, n = 87) were randomized to receive rhIL-3 10 microgram/kg/d (n = 130) or placebo (n = 68) for a maximum of 28 d after ABMT. Several well-known conditioning regimens were used. From day 1 after ABMT patients were treated with placebo or rhIL-3 at a dose of 10 microgram/kg/d by continuous i.v. infusion for 7 d and then by s.c. administration for 21 d or until platelet (50 x 109/l) and neutrophil (0.5 x 109/l) recovery had occurred. Treatment was completed in 54% of the patients in the rhIL-3 group versus 75% in the placebo group (P < 0.004). Adverse events were the main reason for premature discontinuation in the IL-3 group (23% IL-3 v 5% placebo). The median number of platelet transfusions was not significantly different between the IL-3 group and the placebo group (8.0 IL-3 v 6.0 placebo, P = 0.09). Platelet engraftment (>/= 20 x 109/l) was not significantly faster in the IL-3 group (28 d in the IL-3 and 27 d in the placebo group, P = 0.06) and the incidence of haemorrhagic complications was similar in both groups. In patients receiving the full intended dose of rhIL-3, platelet engraftment to >/= 20 x 109/l was delayed (P = 0.007). The median time to neutrophil engraftment was 23 d in the IL-3 and 25 d for the placebo group (P = 0.39). There was no difference in the incidence of major infections. We conclude that treatment with IL-3 has no clinical benefit in patients receiving ABMT for malignant lymphoma.