Summary. Holstein calves, reared from birth under standard conditions, were given various combinations of pmsg-lh or pmsg-hcg at 8 to 9 weeks, or at 17 weeks of age. Follicular development was variable, but averaged fifty-three follicles≥1·0 cm in diameter following administration of either 1500 or 2000 i.u. of pmsg. Ovulation rate was 79% following 50 mg of lh, but it was only 16% following 1500 i.u. of hcg. The presence of young corpora lutea or the administration of progesterone accelerated transport of ova into the uterus and was associated with a reduced percentage of cleaved ova and a lower recovery rate. Liquid semen was superior to frozen semen in initiating cleavage of ova. Under optimum conditions, approximately 75% of the developed follicles ovulated and a similar proportion of ova was cleaved at the time of collection or cleaved in culture. Recovery rate was usually less than 30%.