Background: Binding of the ligand, Granulocyte colony-stimulating factor (G-CSF) to its receptor, the G-CSF receptor (G-CSFR), is instrumental for the action of G-CSF in the different issues. Aim: This study was designed to demonstrate the cellular distribution of G-CSFR in nonhematopoietic tissues of adult rats and the regulation of G-CSFR expression by administration of G-CSF and 90% partial hepatectomy (PH). Methods: Part of the extracellular domain of G-CSFR was sequenced. A G-CSFR specific ssDNA probe was designed. Asymmetric PCR using amino-allyl dUTP and secondary labeling with FITC was established. G-CSFR mRNA expression in bone marrow and nonhematopoietic organs (liver, heart, lung, kidney, intestine, lymph node, spleen and bone marrow) of normal rats was assessed by RT-PCR and Northern hybridization. The cellular distribution of G-CSFR mRNA was detected by fluorescent in situ hybridization (FISH). The G-CSFR protein expression was visualized using immunohistochemistry (IHC). Regulation of the receptor expression subsequent to 90% liver resection (6h, 24h, 7d) with and without G-CSF-treatment were investigated by IHC. Results: G-CSFR mRNA was found in all tested organs of normal rats by RT-PCR, and by Northern blot analysis. FISH and IHC on nonhemaopoietic tissue revealed G-CSFR receptor expression in the cytoplasma of hepatocytes, cardiomyocytes, type II pneumocytes, proximal convoluted tubular cells, single enterocytes in the intestine, acinar cells of the pancreas. G-CSFR expression was induced by G-CSF administration. Upregulation of G-CSFR expression was prominent 6 hours after 90%PH and an additive effect of G-CSF administration and 90%PH could be demonstrated. Conclusions: G-CSFR is expressed in parenchymal cells in adult rats. G-CSFR expression can be upregulated by the administration of G-CSF and by a major surgical trauma as shown in the model of 90% liver resection. G-CSFR expression was most prominent 6 hours after PH and an additive effect of combined G-CSF treatment was revealed. This could indicate a possible biologic significance of G-CSFR in the early phase of repair and regeneration processes.