The effects of increasing postmortem delay (PMD) times on morphological, immunological and functional characteristics of various brain cells both in situ and in vitro were studied in postmortem brain tissue derived from rats with acute experimental allergic encephalomyelitis (EAE). A decline of the brain tissue structure was first noted after a PMD of 6 h. Radial glia in the cerebellum were frequently interrupted and retractions artifacts appeared around brain cells. However, even after the longest PMD interval of 18 h the quality of the cell and tissue structure was still good enough for immunohistochemical characterization. Immunohistochemical staining of frozen and fixed rat brain tissue sections resulted in an enhancement of the immunoreactivity after a PMD of 4 h, using a panel of mono and polyclonal antibodies directed against glial fibrillary acidic protein (GFAP), basement membranes (laminin), brain macrophage antigens (ED1 and ED2), and various immunologically important surface molecules, such as major histocompatibility complex (MHC) class II (Ia) antigen (OX6), CR3 complement receptor (ED8), and leukocyte common antigen (OX1). No increase in staining intensities with the ED1, ED8 and OX6 mAbs specific for macrophage antigens could be detected on brain macrophages that were isolated from brain tissue of rats with EAE obtained after various PMD intervals. Irrespective of the PMD interval, viable astrocyte cell cultures were obtained with comparable staining intensities for GFAP. These cultured astrocytes were capable of ingesting Latex beads and were highly proliferative as measured by BrdU uptake, at all investigated PMDs. Thus, even after long PMD intervals, brain material can be used successfully. Other data suggest that the situation is similar to human brain material, even though the PMD times may be somewhat different.