The intrafo1licular echoes of cumulus oophoruses within ovarian follicles were assessed with the use of ultrasound in 86 women taking part in an in vitro fertilization(IVF) or gamete intrafallopian transfer(GIFT) program, stimulated with pure follicle-stimulating hormone(FSH)/human menopausal gonadotropin(hMG)/human chorionic gonadotropin (hCG). When intrafo1licular echoes were clearly separated from the follicular wall or relatively dispersed within the follicle, they were considered to be a dissociated cumulus, and when they were only slightly prominent from the follicular wall, they were suspected to be a nondissociated cumulus. A cumulus was seen in 62.1% of the follicles larger than 10 mm diameter and 75.1% of them were dissociated. The larger the follicles in size, the more the cumuluses in number and dissociation. The number of follicles and intrafollicular echoes per woman was not different whether or not she would be pregnant, but the number of dissociated cumuluses was significantly more in pregnant women. The number of observed dissociated cumuluses correlated significantly with the number of recovered mature oocytes. When an intrafollicular echo is seen, it can be taken as evidence of a sign of maturity of that particular follicle and oocyte. Ultrasonographic monitoring of intrafollicular echoes and follicular size is very helpful to predict follicular maturation in ovulation stimulation cycles.