PBSCs are usually mobilized using G-CSF with or without chemotherapy. With the emergence of newer mobilizing agents, predicting poor mobilization may allow early intervention and prevent the costs and complications associated with remobilization. We retrospectively evaluated a cohort of 1556 patients seen between January 2000 and September 2008 with multiple myeloma (565; 36%), non-Hodgkin's lymphoma (NHL) (562; 36%), amyloidosis (345; 22%) or Hodgkin's disease (94; 6%), who were initially mobilized with single agent G-CSF. Sensitivity and specificity analysis was used to identify ideal peripheral blood CD34 count (PB-CD34) cutoff points that predicted successful collection. In patients with plasma cell disorders, a PB-CD34 count of 11, 17, 21 and 28/μL by day 4 or 5 was required to collect a target of 2, 4, 8 or 12 million cells/kg, respectively. A CD34 yield of <0.8 million cells/kg on first apheresis also predicted for <2 million CD34 cells/kg. For patients with NHL or Hodgkin's disease, a PB-CD34 count of <6 and <15/μL on day 4 or 5 predicted failure to achieve a target collection of 2 and 4 million cells/kg, respectively. This study suggests that PB-CD34 thresholds should be based on collection target to allow for early intervention and to prevent collection failures.