Over a 5-year period we evaluated 65 myeloma patients aged < or = 55 years as potential candidates for intensive therapy and allogeneic BMT. Twenty six (40%) patients were transplanted; the median duration of disease was 4 months (range 2-58 months) and median number of prior regimens was 1 (range 1-5); all but five patients had chemosensitive disease. Conditioning regimens included combinations of BU+CY+MEL in 14 patients, BUCY2 in eight and CY+TBI in four. Donors were HLA-matched siblings in 19 cases, one antigen mismatched siblings in three and unrelated donors in four. All patients received CsA, plus either methylprednisolone (n = 5) or MTX with or without other agents (n = 19). Grade III or IV regimen-related toxicity (RRT) was relatively infrequent (3 patients) and was not seen in nine patients conditioned with BU (total dose 12 mg/kg) + MEL (100 mg/m2) + CY (90 mg/m2). Grade II-IV acute GVHD occurred in 20 patients, and was the cause of death in three. Chronic GVHD also caused three deaths. Thirteen of 21 evaluable patients (62%) achieved a CR and six achieved a PR. Actuarial progression-free survival (PFS) was 40% (95% confidence interval (CI) 19-61%) at a median follow-up of 14 months (range 3-56 months); the PFS was 52% (95% CI 24-74%) in chemoresponsive patients, compared with 0% in chemoresistant patients (P = 0.0066).(ABSTRACT TRUNCATED AT 250 WORDS)