We analyzed the prognostic factors for a successful mobilization and peripheral blood stem cell collection in a series of 57 consecutive patients with multiple myeloma (MM); a new scoring system to predict an adequate mobilization in this subset of patients was also constructed. A total of 221 aphereses were performed in 57 patients with MM. The median time from diagnosis to mobilization was 12 months (range 4-120). Only one line of chemotherapy was administered before mobilization to 36 patients and two or more to 21. The median number of alkylating chemotherapy cycles was 6 (2-33). Two patients were mobilized in complete remission, 32 in partial response, and 23 in stable/progressive disease. Significant adverse prognostic factors for collecting 2.5 x 10(6) CD34+cells/kg or more were: a period of at least 12 months from diagnosis, at least six cycles of alkylating agents, and a plasma cell infiltration of 20% or more prior to mobilization. Patients with three risk factors had a probability of only 0.38 (95% CI 0.3-0.9) for adequate mobilization. Ten patients failed to mobilize; a period from diagnosis of 12 months or more and female sex were unfavorable factors. Patients with two risk factors had a probability of 0.50 (95% CI 0.2-0.8) for failing the mobilization procedure. These findings indicate that MM patients must be mobilized early in the course of the disease, with minimal disease burden before severe hematopoietic progenitor cell injury due to cumulative therapy.