This study has presented the fine structure changes in the eosinophilic leukocyte in the rat uterus during the estrous cycle. Eosinophils were seen to emigrate into the uterine connective tissues from the blood stream. Just prior to, during estrus, and 1 day postestrus, eosinophilic leukocytes underwent lysis releasing their contents into the extracellular spaces and both whole eosinophils and individual granules from lysed cells were ingested by resident macrophages. No phagocytic activity by eosinophils was observed.
The possible relationship of the turnover of eosinophils to the profound morphologic and chemical changes in the uterus during the estrous cycle was discussed.