Peripheral blood stem cell (PBSC) transplantation (PBSCT) following high-dose chemotherapy is considered to be an effective and curative strategy for patients with certain malignancies. Optimal conditions for collection of PBSC and successful PBSCT, however, are still controversial. We performed 57 leukaphereses after 19 courses of chemotherapy for mobilization of PBSC (semi-high-dose VP-16 alone; 500 mg/m2/day for 3 or 4 days, 13 courses, or conventional chemotherapy; six courses) combined with subsequent G-CSF administration in 13 patients with malignancies (six with lymphoma, five with leukemia, and two with germ cell tumors). Total numbers of the CD34+ cells and CFU-GM obtained by multiple leukaphereses after one course of mobilization therapy were 0.63-168.74 x 10(6)/kg (mean 33.94) and 0.15-56.0 x 10(5)/kg (mean 8.22), respectively. We demonstrated that many cellular components of peripheral blood (PB) on the day of PBSC harvest, especially CD34+ cell, total leukocyte, myelocyte and monocyte counts, were correlated with the numbers of CFU-GM obtained in each leukapheresis. A daily increase of leukocyte counts was another useful indicator for the day of PBSC harvest. We also found that the time when total leukocyte counts in PB recovered to more than 5000/microliters or when CD34+ cells within PB mononuclear cells exceeded 1% was optimal for PBSC harvest. Our results confirmed that the semi-high-dose regimen with VP-16 combined with G-CSF is a safe method which has both antitumor effects and mobilization ability of PBSC in patients with hematological malignancies. PBSCT following various high-dose chemotherapy regimens with or without total body irradiation was also performed in 11 of the 13 patients, and rapid hematologic recovery was observed in all of the patients.