A cytological evaluation is being made of oocytes retrieved from uncultured and cultured rhesus follicles. This includes germinal vesicle chromatin organization, meiosis, and patterns of protein phosphorylation using fluorescence microscopy. Cumulus enclosed oocytes (CEOs) from antral follicles over 500 m were collected in the early and late follicular phase of the menstrual cycle. The effect of the time of collection, hours in culture and different media on meiotic competence were observed. Significantly more oocytes extracted from follicles during the early follicular phase of the menstrual cycle progressed past the unrimmed stage of nucleolar chromatin than from the late phase. After oocyte culture, this difference disappeared. Completion of meiosis increased with hours in culture. The addition of epidermal growth factor to oocyte culture medium increased the percent that became meiotically competent and those that completed meiosis. Freshly isolated oocytes from preantral follicles (<250 m) were incapable of resuming meiosis in culture. Follicle culture from 4 to 8 days