In order to determine the clinical impact of CD34+ cell selected autologous transplantation in multiple myeloma (MM), we have performed a retrospective case-controlled analysis comparing 21 MM patients receiving high-dose melphalan and autologous transplantation with CD34+ peripheral blood stem cells (PBSC) as front-line therapy to 21 control patients receiving unselected products. Case matching was performed using the following criteria: age and beta2-microglobulin at diagnosis and disease status at the time of transplantation. Both cohorts were homogeneous in term of induction treatment and conditioning regimen. Patients were collected for CD34+ selection after priming with G-CSF alone. Significantly fewer CD34+ cells/kg were infused to patients in the selected group as compared to patients in the control group: 2.2 (range 0.5-14.3) vs 9.4 (range 1.1-15) (P < 0.001). The median time to neutrophil recovery > or =0.05 x 10(9)/l was 10 days for the CD34+ group and 9.5 days for the control group (P = 0.357). The median time to platelet recovery > or = 20 x 10(9)/l was 9 days for the CD34+ group and 4.5 days for the control group (P = 0.005). Response rates were comparable in both groups (85.7% in the CD34+ group vs 90.4% in the control group). At 3 years, event-free survival (32% in the CD34+ group vs 39% in the control group) and overall survival (85% in the CD34+ group vs 79% in the control group) were not significantly different. Finally, use of unselected products dramatically reduced the cost of the transplantation procedure. This study shows that CD34+ cell selected autologous transplantation is more expensive than transplantation with unselected products and does not improve the clinical outcome of patients with MM.