Colony-stimulating factors (CSF) are frequently used in cases of cytostatic therapy of patients with testicular cancer assuming that they support hematopoietic recovery and, thus, shorten duration of neutropenia as well as reduce infections. Currently, G-CSF and GM-CSF are clinically used. In the present study efficacy and toxicity of these two drugs were investigated and compared in patients with testicular cancer treated by standard chemotherapy. Studying 83 chemotherapy cycles applied to 31 patients with advanced germ cell tumors the effectivity and the side effects of the two CSF were examined by questioning, clinical evaluation, and blood chemistry studies. G-CSF (480 micrograms subcutaneously (s.c.)) were used in 55 and GM-CSF (400 micrograms s.c.) in 28 chemotherapeutic cycles. The indications consisted in the treatment of leukocytopenia on the one hand and in the prophylaxis in subsequent cycles on the other hand. No difference between the two CSF could be found either with regard to postponement of the next cycle (G-CSF: 6.8 vs. GM-CSF: 7.3 days), or to the number of injections per cycle (G-CSF: 8 vs. GM-CSF: 12.5), or to the leukocyte (G-CSF: 2.1 vs. GM-CSF: 1.6 x 10(3)/microliter) or platelet nadir (G-CSF: 0.5 vs. GM-CSF: 0.5 x 10(5)/microliter; mean values of all cycles, respectively). Both CSF did not seem to influence the production of platelets. However, a difference between the two CSF was demonstrated with respect to the toxicity. Frequency (G-CSF: 38.5% vs. GM-CSF: 69.3%) as well as intensity of side effects causing a change of the drug (G-CSF: n = 1 vs. GM-CSF: n = 7) were lower in the case of G-CSF. In conclusion, these data demonstrate no difference was seen between G-CSF and GM-CSF with respect to the efficacy in patients with testicular cancer treated by standard chemotherapy. However, the use of G-CSF seems to be associated with lower toxicity.