We sought to determine factors that impact on the recovery of platelets after blood cell transplantation in patients with multiple myeloma. We performed retrospective analyses in 51 patients undergoing blood cell transplantation for multiple myeloma. The proportional-hazards model was applied to determine significant risk factors. Of 51 transplants, 14 patients failed to achieve a platelet count of 50 x 10(9)/l. Median time to a neutrophil count of 0.5 x 10(9)/l was 10.5 days. Median time to achieve a platelet count of 50 x 10(9)/l was 32 days. Multivariate analysis revealed that cyclophosphamide and G-CSF priming before collection of hematopoietic precursors (P < 0.001) was a positive predictor of rapid engraftment and prior exposure to melphalan given orally (P = 0.02) was a negative predictor of subsequent platelet engraftment. The number of mononuclear cells collected, the patient's disease status at the time of transplant and the presence of circulating plasma cells in the harvested product did not have a significant impact on time to platelet engraftment. We conclude that cyclophosphamide and G-CSF priming shortened the time to achieve platelet engraftment compared with G-CSF alone. Prior exposure to melphalan delayed platelet engraftment and can lead to complete failure of platelet recovery. Stem cells should be collected before melphalan administration in patients with multiple myeloma who are candidates for possible blood cell transplantation.