The objectives were to test the effects of estradiol treatment of teaser bull mounts on sexual behavior and on quality and quantity of sperm obtained from sires managed as in large commercial AI breeding organizations. In a change-over design, the same teaser bulls were either untreated or treated with estradiol. Five semen-producing bulls were ejaculated twice per day on Tuesdays and Fridays after epididymal reserves were partially depleted. A 15-min period of continuous sexual preparation with three false mounts allowed was standard before each semen collection. All bulls were attracted to and licked the preputial area of the teaser bulls followed by the Flehmen response during the period of sexual preparation. Bulls usually completed the false mounts in < or = 15 min, and all thrusted vigorously with both hind feet moving forward synchronously at this time on 100% of the 80 semen collections. Major differences among bulls and between first and second ejaculates occurred in semen volume, semen concentration, and total sperm collected. An increase of 10% in total sperm output when bulls were exposed to treated teaser bulls could be of commercial benefit. The correlation between total time to first mount for the two ejaculates per bull each day and total sperm collected per bull per day was -.44. Thus, the shorter time to first mount may be useful as a low level predictor of higher sperm out-put per bull.