Expression of beta-trace protein (beta-trace), recently identified as glutathion-independent prostaglandin D synthase (prostaglandin-H2 D-isomerase; EC 5.3.99.2), was localized in paraffin sections of the human brain by in situ hybridization using digoxigenin-labeled antisense cRNA probes. The mRNA for beta-trace was predominantly found in the epithelial cells of the choroid plexus. Hybridization signals were also obtained in some oligodendrocytes, particularly in the white matter. In the leptomeninges, specific signals were found in meningeal macrophages and in single cells of the arachnoid barrier layer. The cells exhibiting hybridization signals with the antisense cRNA probes for beta-trace were identified by counterstaining with antibodies directed against specific cell markers. Additionally, beta-trace mRNA was localized in tubular epithelial and basal cells of the human epididymis and in different cell types within the seminiferous epithelium of the testis.