We retrospectively compared the incidence and clinical characteristics of cGVHD in 37 allo-PBT recipients transplanted between July 1994 and October 1996 and 37 historical control allo-BMT recipients in a case-control study. All patients received a first unmanipulated transplant, graft from an HLA-identical sibling donor, with CsA-MTX GVHD prophylaxis and survived more than 100 days after transplant. PBT and BMT groups were well matched for age, grade of acute GVHD, male patients grafted from female donors, and phase of disease. The median CD34+ and CD3+ cell numbers infused in the PBT group were 5.2 x 10(6)/kg and 307 x 10(6)/kg, respectively. The median time to an ANC greater than 0.5 x 10(9)/l was 16 days (range 11-22) after PBT and 22 days (range 14-36) after BMT (P < 0.001). The median time to a platelet count greater than 20 x 10(9)/l was 15 days (range 6-43) after PBT and 28 days (range 12-68) after BMT (P < 0.001). Median follow-up was 12.3 months (range 5.4-30.3) and 58.7 months (range 4-122.3), for patients receiving PBT and BMT, respectively. Seventeen out of 37 (46%) PBT recipients, vs nine out of 37 (24%) BM recipients developed cGVHD. Actuarial probability of cGVHD at 1 year was 59% (95% CI, 39-79) in the PBT group vs 27% (95% CI, 12-42) in the BM group (P = 0.01). Cumulative incidence estimate of cGVHD was 51% and 25%, for patients receiving PBT and BMT respectively (P = 0.03). Clinical characteristics of cGVHD and response to therapy were similar in both groups, except for a higher incidence of de novo cGVHD in the PBT group. Our results suggest that as compared with BMT, PBT may result in an increased incidence of cGVHD.