Granulocyte-monocyte colony-stimulating factor (GM-CSF) is a member of the hematopoietic growth factor family, promoting proliferation and differentiation of hematopoietic progenitor cells of the myeloid lineage. In recent years, GM-CSF has also proved to be an important neurotrophic factor in the central nervous system (CNS) via binding to the GM-CSF receptor (GM-CSF R). Furthermore, studies on rodent CNS revealed a wide distribution of both the major binding α-subunit of the GM-CSF R (GM-CSF Rα) and its ligand. Since respective data on the expression pattern of these two molecules are still lacking, the present study has been designed to systematically analyze the protein expression of GM-CSF and GM-CSF Rα in the human brain, with particular emphasis on their regulation in Alzheimer's disease (AD). One major finding is that both GM-CSF and GM-CSF Rα were ubiquitously but not uniformly expressed in neurons throughout the CNS. Protein expression of GM-CSF and GM-CSF Rα was not restricted to neurons but also detectable in astrocytes, ependymal cells and choroid plexus cells. Interestingly, distribution and intensity of immunohistochemical staining for GM-CSF did not differ among AD brains and age-matched controls. Concerning GM-CSF Rα, a marked reduction of protein expression was predominantly detected in the hippocampus although a slight reduction was also found in various cortical regions, thalamic nuclei and some brainstem nuclei. Since the hippocampus is one of the target regions of neurodegenerative changes in AD, reduction of GM-CSF Rα, with consecutive downregulation of GM-CSF signaling, may contribute to in the progressive course of neurodegeneration in AD.