The timing of transplantation in chronic myeloid leukaemia is still debated and previous treatment with interferon (IFN) alpha has been reported to be deleterious. We have analysed the outcome of 438 allogeneic transplants performed between 1984 and 1995 and reported to the Société Française de Greffe de Moelle (SFGM) registry. One hundred and two patients (group I) received IFN for more than 6 weeks (median = 9 months) before transplant. Their outcome was compared with 336 other patients (group II) not pretreated with IFN. There were no significant differences between the groups for engraftment and chronic graft-versus-host disease (GVHD) incidence. However, other significant differences included the incidence of acute GVHD > or = 2 at 3 months which was higher in group I (65 +/- 10%) than in group II (38 +/- 5%; P = 0.01). Moreover, disease-free survival (DFS) and overall survival (OS) at 5 years were significantly shorter for group I than for group II (33 +/- 10% vs. 41 +/- 6%; P = 0.005)(95% CI) and (41 +/- 10% vs. 55 +/- 6%; P = 0.002)(95% CI) respectively. After adjustment for patient and transplant covariables in a multivariate analysis, prior IFN was not found to adversely affect transplant outcome.