The purpose of this study was to analyze changes in the T-helper cell 1/T-helper cell 2 (Th1/Th2) balance of peripheral T-helper cells after autologous peripheral blood stem cell transplantation (auto-PBSCT) for non-Hodgkin's lymphoma (NHL) and to evaluate the effects of chemotherapy and granulocyte colony-stimulating factor (G-CSF) on the Th1/Th2 balance. A series of peripheral blood samples from four patients with NHL were collected before peripheral blood stem cell harvest and after auto-PBSCT. Using flow cytometry, Th1 and Th2 cells were identified by their intracellular cytokines: interleukin (IL)-4-/interferon (IFN)-gamma+ and IL-4+/IFN-gamma-, respectively. The Th1/Th2 balance was estimated as the ratio of IL4-/IFN-gamma+ cells to IL-4+/IFN-gamma- cells. Although the Th1/Th2 balance decreased initially, it increased markedly 28 days after the cessation of G-CSF, following auto-PBSCT, in parallel with an increase in lymphocytes. This increase was mainly due to an increase in the proportion of Th1 cells. The Th1/Th2 balance did not change appreciably before PBSC harvest. Serum IFN-gamma increased after auto-PBSCT in three patients. These preliminary data demonstrate that, after auto-PBSCT for NHL, the Th1/Th2 balance decreases initially and then increases after 1 month to levels above pretreatment levels and that the effects of chemotherapy and G-CSF on the Th1/Th2 balance are negligible before PBSC harvest. Further evaluation of the Th1/Th2 balance after allogeneic PBSCT at the single-cell level should be undertaken using this method.