OBJECTIVE To determine the presence and localization of leukocyte subsets in the human follicular wall and in the corpus luteum (CL) throughout the menstrual cycle. METHODS Tissue was obtained by biopsy at laparoscopy. Frozen sections were labeled with a panel of monoclonal antibodies against leukocyte subtype markers and detected by immunohistochemical methods. METHODS Infertility clinic in large teaching hospital. METHODS Eighteen women who underwent diagnostic laparoscopy. Women with abnormal endocrinology, endometriosis, or ovarian disease were excluded. RESULTS Macrophages and neutrophilic granulocytes were present in high numbers in the collagen-rich tissues, including the thecal layer, of the follicle wall. At ovulation, there was a marked increase in the density of these cells in the follicle wall, especially in the thecal layer. In the CL, there was a higher density of macrophages (2- to 3-fold) and neutrophils (3- to 5-fold) in the theca lutein area compared with the granulosa lutein area. There were no significant changes in the density of these cell types when early and late luteal phase were compared, but the density of macrophages were markedly elevated in regressing CLs obtained during the subsequent follicular phase. T lymphocytes were present in low numbers in the follicle wall and in the CL, and no variation in the density was detected throughout the menstrual cycle. CONCLUSIONS Macrophages and neutrophilic granulocytes are present in high numbers in the follicle wall and are further increased in the theca at ovulation, suggesting an active role for these leukocyte subtypes in tissue remodeling during the ovulatory process. Macrophages and neutrophils are also abundant in the CL, and an increase in the macrophage density at CL regression could imply a role for these cells in luteolysis.