The superovulatory response was followed up in 14 beef heifers by rectal palpation and by ultrasonographic examinations of the 28 ovaries, on day 7 after superovulation induced with PMSG (ovulation = day 0). Using a B-mode ultrasound instrument (Aloka Echo Camera SSD-210-DX II) equipped with a 5 MHz linear transrectal transducer, ultrasonography was found to be more reliable than rectal palpation. A significantly higher number of follicles (P < or = 0.049) was identified by ultrasound scanning than by rectal palpation of the ovaries: follicles were more easily differentiated from cysts using ultrasonography, since each fluid-filled vesicle was accurately measured on the screen and presented on the echogram.