Objective To detect and localize the expression of macrophage colony stimulating factor (M CSF) in human luteinized granulosa cells and investigate the effects of follicle stimulating hormone (FSH) on M CSF production by human luteinized granulosa cells in vitro Methods Human luteinized granulosa cells were isolated from follicular fluid of superovulated infertile patients undergoing intracytoplasmatic sperm injection Some of the luteinized granulosa cells were used for detecting M CSF by immunocytochemical staining (ABC method) Most of them were cultured with HAM′s F 10 medium alone or plus various concentrations of FSH (2, 5, 15, 25 IU/ml) The media were collected after 72 hours and their M CSF contents were measuered by a solid phase enzyme linked immunosorbant assay Results About 80% of the luteinized granulosa cells were positively stained for M CSF antibody The immunoreactive signals of M CSF were specially located in the cytoplasma of the luteinized granulosa cells No immunoreactivity of M CSF was observed in vaginal squamous epithelial cells through contaminations during transvaginal oocyte retrieval The concentration of M CSF in cultured luteinized granulosa cells medium without FSH stimulation was low However, addition of 2, 5, 15, 25 IU/ml concentrations of FSH caused significant dose dependent increases of M CSF production after 72 hours culture by luteinized granulosa cells ( P