G-CSF enhances the division, maturation and release of granulocyte precursor cells. The shortening of chemotherapy-induced leukopenia via G-CSF is well documented in literature, with fractionated radiotherapy alone one finds a distinct increase of the granulocyte level. There are only few results for combined simultaneous radiochemotherapy.In the Department of Radiotherapy of the University of Erlangen 102 patients were treated with G-CSF since 1992. Twenty-eight patients (31 applications) undergoing radiotherapy only (n = 4) or combined simultaneous radiochemotherapy (n = 27) received G-CSF interventional daily. These results are presented and discussed. Indications for the application of G-CSF were severe leukopenia below 1000/mm3 (level IV according to WHO) or rapid decreasing leukocytes during therapy. G-CSF was not applied during chemotherapy and terminated at least 24 h before the next chemotherapy cycle. r-metHuG-CSF (Filgrastim, Neupogen) was used subcutaneously. Documented were the duration until the leukocyte increase, neutrophil granulocytes, thrombocytes, interruption of radiotherapy, febrile episodes and side effects.In case of severe leukopenia (< 1000/mm3 n = 16) the leukocytes increased after 3 days of G-CSF application, the radiotherapy was interrupted in 2 cases, terminated in 1 case. Four patients had lever before during G-CSF 4 additional febrile episodes occurred. If G-CSF application was started between leukocyte levels of 1000 and 1500/mm3 after 1 day the leukocytes increased in 9 of 10 cases beyond the starting level. Interruption of radiotherapy was not necessary. Only 1 febrile episode occurred (1/11). There were no relevant side effects of G-CSF.Rapidly developing or severe leukopenia during radio(chemo)therapy are indications for an interventional application of G-CSF. The leukocyte level for the start of G-CSF should be chosen so that without G-CSF an interruption of therapy or a level IV leukopenia seems to be unavoidable.