We investigated, by means of in situ hybridization with a digoxigenin-labelled RNA probe, the expression of the low-affinity p75 nerve growth factor receptor (NGFR) in the developing pituitary primordium of the rat. In 13-day pc embryos, intense staining of p75 NGFR mRNA was present in the cytoplasm of all cells of Rathke's pouch. In day-17 pc embryos p75 NGFR expression was present primarily in the cells of the intermediate lobe. In the newborn rat pituitary only very weak staining was observed, predominantly in the intermediate lobe. In neural structures the staining at day 13 pc was comparable to that of day 17 pc. Since p75 expression is seen very early during pituitary development and declines during the time the expression of pituitary hormonal phenotypes are steadily increasing, we suggest that the p75 NGFR expression in Rathke's pouch may play a temporally defined role in the commitment rather than in the differentiation of the various pituitary cell types.