The serum levels of soluble interleukin 2 receptors (sIL-2R) were determined in 19 patients who received high-dose chemotherapy and an autologous or syngeneic bone marrow transplant (BMT) for treatment of Hodgkin's disease (n = 18) or non-Hodgkin's lymphoma (n = 1). Twelve patients received granulocyte colony-stimulating factor (G-CSF) from day 0 or day +1 after autologous BMT until the white blood cell count had been stable for 9 d above 1 x 10(9)/l, the remaining seven patients did not receive growth factors. In all G-CSF-treated patients the sIL-2R levels increased steadily in the early post-transplant course, even in the absence of infection. This increase was statistically significant 2-4 d prior to the appearance of leucocytes in the peripheral blood (median 340 pM versus median 256 pM immediately after BMT, P < 0.025) and peaked with the appearance of first peripheral blood leucocytes (median 536 pM, P < 0.001). Cessation of G-CSF administration resulted in a decline of sIL-2R levels. In contrast, five of seven patients without G-CSF treatment did not exhibit an sIL-2R increase before or at the time of engraftment. Infection was associated with a rise of sIL-2R levels. A correlation between sIL-2R levels and total leucocyte count, lymphocyte count, or CD25+ lymphocyte count was not evident. These data suggest that after autologous BMT G-CSF induces increased sIL-2R levels, which occur independent of lymphocyte activation. This may be compatible with involvement of immature bone marrow cells in G-CSF-induced sIL-2R release.