The feasibility and efficacy of autologous stem cell transplantation (auto-SCT) in patients aged > or = 70 years was analysed. Newly diagnosed (n = 34) and refractory multiple myeloma (n = 36) patients were studied. The median age was 72 years (range: 70-82.6). CD34+ cells were mobilized with chemotherapy and granulocyte colony-stimulating factor (G-CSF) (n = 35) or G-CSF alone (n = 35), yielding medians of 11.8 x 10(6) versus 8 x 10(6) cells/kg respectively (P = 0.007). Because of excessive mortality (16%) in the first 25 patients who received melphalan 200 mg/m2 (MEL-200), the dose was subsequently decreased to 140 mg/m2 (MEL-140). Median times to absolute neutrophil count (ANC) > 0.5 x 10(9)/l and to platelets > 20 x 10(9)/l were 11 and 13 d respectively. Thirty-one patients (44%) received tandem auto-SCT. Complete remission (CR) was 20% after the first SCT and 27% after tandem SCT. Median CR duration was 1.5 years and was significantly longer for patients with < or = 12 months of prior chemotherapy (2.6 versus 1.0 years, P = 0.0008). The 3-year event-free survival (EFS) and overall survival (OS) (+ standard error, SE) were projected at 20% + 9% and 31% + 10% respectively. Tandem SCTs positively affected EFS (4.0 versus 0.7 years; P = 0.003) and OS (4.0 versus 1.4 years; P = 0.02) compared with single auto-SCT. In conclusion, MEL-140 is less toxic and appears equally as efficacious as MEL-200 in elderly patients. The benefits of tandem SCT in this patient population need further evaluation in a randomized trial.