Serum levels of monokines, including macrophage colony-stimulating factor (M-CSF), tumor necrosis factor-alpha (TNF-alpha), interleukin-1 alpha (IL-1 alpha) and IL-1 beta (IL-1 beta), were measured in patients with chronic renal failure in an attempt to clarify the kinetics of these cytokines in the course of renal anemia. M-CSF was the only monokine detectable in the serum from all patients as well as healthy donors, making this cytokine feasible and reliable for serial evaluations. On all occasions, the level of M-CSF in uremic patients was significantly higher than that in healthy donors (29.4 +/- 12.3 vs. 5.5 +/- 1.1 ng/mL). In patients undergoing hemodialysis, the serum level of M-CSF was greater than that in patients undergoing continuous ambulatory peritoneal dialysis or in uremic patients without dialysis therapy. No difference was observed, however, in the levels of IL-1 alpha, IL-1 beta and TNF-alpha levels in these groups. Patients with severe anemia were subsequently treated with 60 to 80 U/kg per week of human recombinant erythropoietin (rhEpo) for 3 months. After this replacement therapy, hemoglobin levels increased with a variable change ranging from 0 to 3.5 g/dL. The pretherapy M-CSF level, however, was found to predict statistically the response to the therapy (p < 0.05). Patients with a lower pretherapy value responded better to rhEpo therapy; those with a higher level showed a minor degree of response. From these results, we postulate that the elevated M-CSF serum level in uremic patients is in part a consequence of the dialysis procedure and that rhEpo therapy is more effective in patients who are under sophisticated dialysis protocol and have a lower M-CSF level.