Allogeneic peripheral blood progenitor cell transplantation (alloPBPCT) is increasingly used as an alternative to bone marrow transplantation (alloBMT). Early data suggest that the incidence and severity of acute graft-versus-host disease (GVHD) following alloPBPCT is no higher than that seen with alloBMT, despite the increased number of cytotoxic T cells infused with mobilised blood. We compared 12 patients undergoing alloPBPCT with 12 well-matched alloBMT controls. All patients received identical GVHD prophylaxis. No T cell depletion or CD34 purification was performed. Median engraftment times for neutrophils >0.5 x 10(9)/l and platelets >20 x 10(9)/l were 14 and 12 (alloPBPCT) and 21 and 23 days (alloBMT), respectively (P = 0.0035 and P = 0.002). There was no difference in antibiotic requirements (P = 0.83), platelet support (P = 0.59) or days in hospital (P = 0.51), After alloPBPCT, five patients developed greater than or equal to grade II acute GVHD vs five patients after alloBMT (P = 0.99), There was one death (alloBMT) at 100 days and three at 1 year (all due to relapse). There was one death at 100 days with alloPBPCT, and 11 patients remain alive (range 9-21 months) to date. Chronic GVHD occurred in five patients in the PBPC arm and one patient in the BM arm (P = 0.14). This case-controlled analysis indicates that alloPBPCT results in more rapid engraftment kinetics but in no significant difference in transplant-related morbidity or mortality. There is no difference in the incidence of acute GVHD. However, there is a trend towards increased incidence of chronic GVHD in patients allografted With PBPC. Prospective randomised trials are required to determine further the role 1 of alloPBPCT.