Estrogen receptors (ER) are widely distributed in the central nervous system (CNS). Recent studies, to date in rat only, have shown that ER are also expressed in neurons of the dorsal root ganglia (DRG) where they appear to have functional roles. However, no data yet exists about estrogen receptors in the embryonic DRG. In the present study, immunocytochemical staining for ER in the DRG of chick embryos from day 6.5 to 18.5 (Hamburger and Hamilton St. 30-45) of incubation was performed. ER+ cells were first consistently observed at day 8.5 (St. 34), more concentrated in the ventral-lateral portion of the DRG. From day 8.5 to 12.5 (St. 38), the density of ER+ cells and the staining intensity increased, with no obvious changes from day (E) 12.5 to 18.5. Although ER is detected mainly in the cytoplasm of embryonic DRG neurones, ER+ cells with nuclear staining are sometimes observed and gradually increase in number during development. ER-immunoreactivity in the DRG at cervical, thoracic and lumbo-sacral levels is similar and no obvious differences in staining were observed between male and female embryos. ER+ neurons are also present in the sympathetic ganglia from E8.5 and some primary spinal motoneurons are ER+ beginning at E14.5. The results suggest that estrogen may play a role in the embryonic development of the DRG.