We performed a sequential study comparing two regimens, cyclosporine-methotrexate (CsA-MTX) and cyclosporine-methotrexate-methylprednisolone (CsA-MTX-MP) for graft-versus-host disease (GVHD) prophylaxis in patients undergoing matched unrelated donor bone marrow transplantation (MUD BMT). Study end-points were the development of GVHD, various infectious complications and survival. Twenty nine patients with malignant hematologic disease without HLA-compatible family donors were treated between May 1990 and November 1993. All donors were volunteers from the National Marrow Donor Program (NMDP) serologically HLA-A-A, B and DR identical. MLC reactivity and high resolution DR DNA typing were not used to exclude donors. Sixteen patients received CsA-MTX and 13 patients received CsA-MTX-MP. CsA and MTX doses were the same in both groups: CsA 1.5 mg/kg i.v. over 2h every 12h beginning the day prior to transplant (day-1) and MTX 10 mg/m2 i.v. bolus on days +1, +3 and +6 with leucovorin on days +2, +4 and +7. MP was administered at a dose of 0.25 mg/kg i.v. every 12h beginning on day +7 and increased to 0.5 mg/kg on day +14. Beginning on day +35 MP and CsA were tapered 5% per week with targeted discontinuation at 6 months. Both groups were comparable for primary disease, preparative regimen, recipient age (median 33 VS 33 years), donor age (median 39 vs 39.5 years), donor-recipient sex, donor ABO mismatch and serologic CMV positivity. All patients received similar supportive care.(ABSTRACT TRUNCATED AT 250 WORDS)