The localization of progesterone receptor (PR) in the ovaries of sexually immature chickens during the post-hatching period was studied by immunohistochemistry. On day 1 after hatching, nuclear PR staining was observed distinctly in germ cells and in the germinal epithelium. The PR immunoreactivity in germ cells was maximal on day 7 and the PR expression progressively and significantly increased in the germinal epithelium throughout the 150 days long period. The PR presence was also evidenced since the 7(th) day in medullar fibroblasts and since the 30(th) day in inter-follicular fibroblasts and in smooth muscle fibres and in these cell types, the staining intensity coupled to the proportion of positive cells (allowing the calculation of the quick score) tended to slightly increase according to time but not significantly. Irrespectively of the post-hatching delay, the highest quick score was recorded for the germinal epithelium. By contrast, granulosa and theca cells surrounding the primary and pre-vitellogenic follicles as well as interstitial and medullar lacunar channel cells appeared PR negative since the 15 day. These results indicate that the PR localization within the different ovarian cell types was regulated in chicken according to the follicle developmental stage and by the steroidogenesis capacity.