Transplant related mortality and relapse after bmt have a negative influence on the outcome of patients transplanted for acute leukaemia in first remission. Transplant related mortality includes graft-versus-host disease, infections and graft failure. To prevent gvhd and associated infections without increased graft rejection, a protocol of combined in vivo/ex vivo T-cell depletion (Campath IgG 20 mg i.v. for 5 days and Campath IgM T-cell depleted graft) with no further immunosuppression was initiated. Up to now 22 adult patients (median age 39 years, range 21 to 51) have been transplanted. One graft failure most probably due to persistent leukaemia, three acute gvhd (grade I) and no chronic gvhd occurred. Two patients relapsed after bmt and died. Two further patients died due to idiopathic interstitial pneumonitis and acute liver failure, respectively. Eighteen patients are alive in complete remission. With a median follow up of 13 months (1-30) the probability of survival is 78%, disease free survival is 80% and transplant related mortality is 10%. We compared these results with 3 historical control groups with different regimens of gvhd prophylaxis. 1. MTX group (n = 15): With a median follow up of 135 (115-147) months after bmt the probability of survival is 40%, disease free survival is 40% and transplant related mortality is 60% (mainly gvhd and infection). 2. Campath group (only ex vivo T-cell depletion n = 25): With a median follow up of 86 (62-102) months probability of survival is 52%, disease free survival is 43% and transplant related mortality is 36% (mainly rejection and infection).(ABSTRACT TRUNCATED AT 250 WORDS)