Fifty-six patients with chemosensitive NHL were studied to assess factors affecting mobilization and peripheral blood stem cell (PBSC) collection: all were mobilized with high-dose cyclophosphamide and etoposide and G-CSF 5 microg/kg/day. None of them had bone marrow involvement at the time of mobilization or a history of extended field irradiation. Previous chemotherapy regimens were divided into two groups: moderately myelotoxic chemotherapy (MMC) and highly myelotoxic chemotherapy (HMC). The adequacy of the PBSC harvest was not associated with age, gender, a past history of bone marrow involvement or disease status. In contrast, the number of MMC cycles (n(MMC)) and the number of HMC cycles (n(HMC)) were both significant (P = 0.009 and P = 0.0004, respectively) and were used to compute a score predictive of a successful PBSC harvest: SCORE = n(MMC) + 4 n(HMC). The estimated successful PBSC collection rate was greater than 80% in patients with a score ranging from 0 to 15 and dropped rapidly to below 20% in patients with a score exceeding 25. This scoring system may help to determine the timing of PBSC mobilization in patients with a score below 15 and suggests that new PBSC mobilization procedures should be investigated in other patients. Bone Marrow Transplantation (2000) 25, 495-499.