The aim of this study was to determine whether the population of mitotic cells changes in correlation with apoptotic cell population in follicular tissues during atresia of white follicles in hens. Hens were injected with 5-bromo-2'-deoxyuridine (BrdU) 1 h before tissue collection. The small white follicles were classified as healthy follicles and as early or late atretic follicles by histological observation. Mitotic and apoptotic cells were determined by immunocytochemistry for BrdU and terminal deoxytranceferase-mediated dUTP nick end labeling (TUNEL), respectively. The BrdU labeling was observed in some of the granulosa cells and thecal fibroblast-like cells in healthy follicles, whereas the population of the labeled cells was reduced in the granulosa and theca layers of atretic follicles. The image analysis confirmed that the frequency of BrdU-positive cells declined significantly in the granulosa and theca layers of early atretic follicles compared with those of healthy follicles. In contrast, the TUNEL-positive cells were negligible in healthy follicles. However, they were localized in the granulosa and theca layers of early and late atretic follicles, and those in the theca layer were more inside than outside. The frequency of TUNEL-positive cells was significantly increased with the progress of atretic changes. These results suggest that the population of mitotic cells decreases in association with increase of apoptotic cells during the atretic process of white follicles.