While abundant data exist documenting variables associated with early platelet engraftment after autologous PBPC transplantation, data concerning later sustained platelet engraftment is sparse. We retrospectively examined a series of 80 patients undergoing autologous PBPC transplantation with respect to their platelet count 6 weeks after transplant. Underlying diagnoses included breast cancer (n = 33), non-Hodgkin's lymphoma (n = 32), Hodgkin's disease (n = 9), and other hematologic malignancies (n = 6). Patients received G-CSF for PBPC mobilization and collected a target threshold number of 2.0 x 10(6) CD34+ cells per kilogram. A univariate analysis revealed that a diagnosis of breast cancer, fewer courses of prior chemotherapy, younger age and complete remission were associated with a higher 6-week platelet count. Additionally, the ability to collect the threshold number of CD34+ with fewer sessions of leukapheresis was also associated with a higher 6-week platelet count. The platelet count and the white blood cell count at the initiation of PBPC collection was also associated with a higher 6-week platelet count. A multivariate analysis revealed a higher platelet count on the first day of pheresis, fewer phereses required to collect 2 x 10(6) CD34+ cells per kilogram, and a diagnosis of breast cancer were all associated with a higher 6-week post-transplant platelet count. Seven patients failed to reach a 6-week platelet count of 30 x 10(9)/l and an additional five patients had a platelet count of 30-50 x 10(9)/l. We conclude that underlying clinical characteristics, as well as hematologic variables at the time of PBPC collection, influence later, sustained platelet engraftment. A percentage of patients have poor sustained platelet engraftment and may be candidates for new cytokines that specifically target megakaryocyte growth and development.