Oligodendrocytes and astrocytes were isolated from normal adult human brains 3-15 h postmortem using a Percoll density gradient centrifugation and were cultured for 10-135 days. The presence of HLA-DR(Ia) antigens on the surface of these human oligodendrocytes and astrocytes was studied using double immunofluorescence procedures. Only half of separate culture series (6/12 donors) contained HLA-DR-positive oligodendrocytes, while all of the culture series (12/12 donors) revealed HLA-DR-positive astrocytes. Among the HLA-DR-positive cultures, 4-16% of galactocerebroside-positive oligodendrocytes and 9-24% of GFAP-positive astrocytes were found to immunoreact with HLA-DR antibody. The presence of Ia antigens on the surface of certain populations of oligodendrocytes and astrocytes may be important in the induction of an immune response to these cells.