In this study, ultrasonography was used to monitor the superovulation progress in ewes in order to exclude animals with low or pathological ovarian response. Ovaries of 17 mixed-breed ewes, superovulated with pregnant mare's serum gonadotropin (PMSG), were scanned daily by transrectal ultrasonography over a period of 10 days around oestrus. Plasma progesterone concentrations were measured daily. On the last day of the examination period, a laparoscopic examination of the ovaries was performed. The dynamics of the follicles and corpora lutea (CL) could be followed clearly. Animals with follicles >8 mm at the day of insemination (Day 0) showed a progression of this status until Day 5. No prediction of the ovulation rate was possible at this time. At Day 5 the number of CL was detected with an acceptable accuracy. It is recommended that a routine scanning of the ovaries prior to insemination, selecting donors with follicles between 4 and 8 mm diameter and no follicles larger than 8 mm for insemination. An ultrasonographic examination prior to embryo recovery (Day 5) allows the exclusion of donors with low ovulation rates (1-2 CL), avoiding unnecessary interventions.