Haemopoietic growth factors are accepted as accelerating haemopoietic recovery after bone-marrow grafting, yet no large randomised trials have been published that convincingly show benefit. Lenograstim (glycosylated recombinant human granulocyte colony-stimulating factor) was given to 315 patients after bone-marrow transplantation in a prospective randomised placebo-controlled multicentre trial. 1 day after bone-marrow infusion, 163 patients received lenograstim 5 micrograms/kg per day by 30-min infusion, and 152 patients received placebo daily for 28 days or until neutrophil recovery. 137 patients had lymphoma, 35 myeloma, 85 acute lymphoblastic leukaemia, and 58 a solid tumour. Patients were stratified by age and by type of bone-marrow transplantation (BMT). Neutrophil recovery to above 10(9)/L for 3 consecutive days was seen earlier in lenograstim-treated patients (16 vs 27 days, p < 0.001). Time to neutrophil recovery above 0.5 x 10(9)/L was reduced (14 vs 20 days, p < 0.001). The difference was significant both in autograft (20 vs 14 days, p < 0.001) and allograft (20 vs 14 days, p < 0.01) patients, in children (20 vs 13 days, p < 0.001), and adults. Lenograstim-treated patients had fewer days of infection, and of antibiotic administration, and also spent less time in hospital. However, clinical and microbiological sepsis was similar in both groups. There was no significant toxicity ascribed to lenograstim. Survival was the same at days 100 and 365. In patients undergoing autologous or allogeneic BMT for neoplastic disease, lenograstim significantly reduced duration of neutropenia and led to earlier hospital discharge.