Sulfation plays a major role in regulating the activity of various neurosteroids, including pregnenolone and dehydroepiandrosterone. The present report describes the immunohistochemical distribution of two enzymes involved in the control of neurosteroid sulfation, hydroxysteroid sulfotransferase (HST) and unconjugated steroid enzyme sulfatase (STS), in the brain of the European green frog Rana esculenta during development. HST and STS immunoreactivity were detected from stage VIII-XII. At this early stage, HST-positive fibers were seen in the glomerular layer and the basal rhombencephalon. Subsequently, at stage XIII-XV, HST- and STS-immunoreactive fibers were vizualized in the accessory olfactory bulb. At stage XVI-XVIII, STS-positive cell bodies were observed in the periventricular region of the diencephalon. These observations indicate that the enzymes controlling sulfation of hydroxysteroids are expressed in the frog brain during development.