We tested the hypotheses that: (1) the superstimulatory response is related to the intrinsic number of follicles recruited into a follicular wave; and (2) the number of follicles recruited into a wave is correlated to the number of follicles recruited into the successive wave. A positive correlation will form the basis of a test for predicting the superstimulatory response. Cows (n = 141) were treated with estradiol and progesterone to synchronize follicular wave emergence (first synchronization) and ranked according to the number of follicles > or =2mm at wave emergence to select the upper and lower 10% of the herd. Follicular wave emergence was synchronized again in the high-end (n = 16) and low-end (n = 20) groups (second synchronization), and cows were treated with FSH twice daily for 3 days. High-end cows had a greater number of follicles (P < 0.001) than low-end cows at the time of wave emergence after both the first and second synchronizations in the 2-3 and 4-6mm categories. The numbers of 2-3 and 4-6mm follicles at wave emergence after the first and second synchronizations were positively correlated (P < 0.001; r = 0.77 and 0.71, respectively). Endogenous FSH peak at the time of wave emergence was higher in the low-end group than in the high-end group. Superstimulatory treatment resulted in more than double the number of follicles (P < 0.003) in the 5-7mm and > or =8mm categories in the high-end group than in the low-end group (16.8 +/- 2.2 versus 8.1 +/- 0.9 and 22.7 +/- 4.1 versus 9.7 +/- 1.6, respectively). The number of follicles > or =5 and > or =8mm at the end of superstimulation was positively correlated (P < 0.001) with the total number of follicles > or =2mm at the time of wave emergence after both the first (r = 0.64 and 0.54, respectively) and second ( r = 0.65 and 0.5, respectively) synchronizations. Based on the results of this study, the superstimulatory response can be predicted by the number of follicles > or =2mm at wave emergence. For practical purposes, practitioners can expect the number of follicles > or =5mm after ovarian superstimulation to be approximately 71% of the number of follicles > or =2mm at the time of wave emergence. Results validated the proposed simple ultrasound-based test for predicting the superstimulatory response of individual cows.