The aim of this work was to monitor and compare ovarian follicular dynamics during estrous cycle in heifers and early postpartum lactating high yielding Holstein cows bred in ČR. The ultrasound machine with 7,5 MHz rectal linear probe was used and digital records were retrospectively analyzed on PC. In 2 wave cycles we found statistically significant differences between heifers and cows when evaluated emergence of 2nd growth wave, size of dominant and ovulatory follicle on 1st and 2nd wave. Differences in follicular dynamics were found in cows exhibiting 3 follicular growth waves (estrous cycle length, emergence of 3rd growth wave, number of follicles on 1st and 3rd wave and size of dominant follicle on 2nd wave). When we compared experimental groups of heifers and cows we found statistically significant differences too (number of follicles, size of dominant and ovulatory follicle). Based on these findings we can claim that a differences in ovarian follicular dynamics between heifers and cows exists.