We conducted a prospective, randomized, multicentre clinical trial comparing the effects and costs of GM-CSF as an adjunct to intensive chemotherapy in elderly patients with acute myeloid leukaemia (AML). The patients were randomized to either daunomycin-cytosine arabinoside (control arm: n = 161) or daunomycin-cytosine arabinoside with GM-CSF (GM-CSF arm: n = 157). The primary end-point was the effect of GM-CSF on the percentage of complete remissions (CR). Survival duration, disease-free survival, quality of life and costs were evaluated separately. CR after remission induction treatment was achieved in 55% of the patients in the control group and in 56% of the patients in the GM-CSF group (P = NS). The duration of survival and disease-free survival at 2 years after randomization were estimated at 22% and 19% for the control group and 22% and 14% for the GM-CSF group (P = NS). Considering the short-term quality of life, the administration of GM-CSF resulted in more problems with regard to depressed mood, diarrhoea and rash/eczema. With regard to the long-term quality of life there were no significant differences between the two groups. The average costs of the primary treatment were higher in GM-CSF-treated patients than in the control group, i.e. US$40782 and US$34465, respectively (P < 0.01). The costs during the follow-up period did not differ between the two groups. The results of this randomized clinical trial indicate that daunomycin-cytosine arabinoside plus GM-CSF is not a cost-effective treatment strategy when compared with daunomycin-cytosine arabinoside alone.