Distribution and characteristics of mast cells have been studied in the ovaries of 5 and 17 week old chickens. 2. Mast cells were mainly present in the stroma, hilum and theca of normal and atretic follicles. No significant age-related differences in percentage distribution of mast cells were observed in the stroma and hilar regions of the ovary. However, the percentage of mast cells associated with follicles in both age groups was significantly less compared to stromal and hilar regions. 3. The number of mast cells present in the theca of normal and atretic follicles of stage 301 to 500 microns increased significantly compared to the preceding stages in 17-week old chicken ovaries. Moreover, the number of mast cells associated with the follicles of this stage in 17-week old chick ovaries was also higher compared to 5-week old chicken ovaries. 4. The mast cells showing variable shapes were divided into two types: compact and degranulating. More degranulating mast cells were observed in the 17-week old chicken ovary compared to those observed at 5-weeks.
