This study was undertaken to evaluate the relationship between the time to recovery of peripheral blood counts and CD34+ cells in the peripheral blood (PB) and apheresis collections of patients undergoing intensive chemotherapy followed by rhG-CSF. Twenty-three patients with a median age of 42 years (range 17-64) with malignancies underwent peripheral blood stem cell (PBSC) collection after cyclophosphamide (CY) 4 g/m2 and etoposide (600 mg/m2) followed by rhG-CSF (10 microg/kg/day). The WBC, platelet counts, CD34+ cell counts per ml of PB, and CD34+ cells in apheresis products were followed in all patients. The relationship of the time to recovery of WBC > 1,000/microl, >3,000/microl, >10,000/microl and platelets >20,000/microl and 50,000/microl was compared to the average daily CD34+ cells/ml in each patient using the Spearman Correlation test. The tempo of recovery of WBC and platelets were highly correlated with the average CD34+ cell count in blood. In order to derive some useful guidelines for the timing of apheresis, the patients were divided into two groups, early recover (ER) and late recover (LR) based on the median time (day 10) to reach WBC count greater than 1,000/microl. ER patients had an average daily PB CD34+ cell count of 9.04 x 10(4)/ml (range 0.44-17.5) and a median yield of CD34+ cells of 10.43 x 10(6)/kg (range 0.60-25.95) compared to LR patients, who had 1.87 x 10(4)/ml (range 0.32-5.44) in the PB (P = .001) and a yield 3.20 x 10(6)/kg CD34+ cells (range 0.037-9.39) (P = .001). Patients recovering their WBC to 1,000/ml within 10 days of completing this regimen may undergo PBSC collection and achieve minimum-target cell doses of >2.5 x 10(6) CD34+ cells/kg--100% of the time.