Several agents, used either alone or in combination, have been shown to boost absolute numbers of PMLs and CD34(+) stem cells in PB. In this study, we compared the effects of three different treatments, G-CSF, HDMP, and G-CSF + HDMP, for neutropenic patients (absolute PML count < 0.5 x 10(9)/l) who were on maintenance therapy for ALL with a control group who received no treatment. Hematological parameters, PB-CD34(+)33(-) and -CD34(+) HLA-DR- stem cell numbers, and serum IL-3 levels were measured prior to, and a week after, the first day of treatment. WBC and absolute PML counts were significantly increased compared to pretreatment values in all treatment groups. However, peripheral CD34(+)33(-) and CD34(+) HLA-DR- stem cell numbers and serum IL-3 levels were increased significantly only in the G-CSF group. There was also a significant increase in serum IL-3 levels in the G-CSF + HDMP group. This study suggests that G-CSF may induce an increase in peripheral stem cell numbers, and that it supports hemopoietic recovery by increasing IL-3 in patients with chemotherapy-induced neutropenia. (C) 1999 Elsevier Science Ltd. All rights reserved.