The use of primed peripheral blood progenitor cells (PBPC) has improved platelet engraftment following autologous bone marrow/PBPC transplantation (ABMT). The thrombocytopenia associated with ABMT generally lasts 14-18 days, and is associated with variable platelet transfusion requirements. Little, if any, data exist examining prognostic parameters for platelet transfusion requirements during autologous transplantation. We retrospectively examined 286 consecutive patients undergoing autologous transplantation from 1 January 1994 to 1 June 1996 with respect to platelet engraftment and platelet transfusion requirements. One hundred and fifty four patients were transplanted for breast cancer (54%), 72 for non-Hodgkin's lymphoma (25%), 35 for Hodgkin's disease (12%), 13 for acute leukemia (5%), eight for myeloma (3%), and four for other malignancy (1%). The median age was 44. All patients received cytokine priming, usually with G-CSF, for the procurement of PBPC. The median number of CD34+ cells collected was 4.3 x 10(6)/kg. All patients received a chemotherapeutic preparative regimen and all received an autologous transplant using PBPC alone. The median time to a platelet count of 20 x 10(9)/l was 13 days. Patients beginning the transplant with a less than normal platelet count (less than 150 x 10(9)/l) engrafted in 17 days, and received a median number of seven platelet transfusions, as compared with platelet engraftment of 12 days, and four platelet transfusions, for patients beginning the transplant with a normal platelet count (P = 0.001). Both groups of patients received an equivalent dose of CD34+ cells. We conclude that thrombocytopenia at the initiation of autologous transplantation is associated with increased platelet transfusion requirements, independent of the dose of CD34+ cells infused.