The objective of this study was to determine the effects of progesterone and cloprostenol (a PGF(2alpha) analogue) on ovarian follicular development and ovulation in prepubertal heifers. In Experiment 1, crossbred Hereford heifers (Bos taurus; 10 to 12 mo old, 255 to 320 kg) were assigned randomly to three groups and given (1) an intravaginal progesterone-releasing insert (CIDR; P group, n=13); (2) a CIDR plus 500 microg cloprostenol im (PGF(2alpha) analogue) at CIDR removal (PPG group, n=11); or (3) no treatment (control group, n=14). The CIDR inserts were removed 5 d after follicular wave emergence. Progesterone-treated heifers (P and PPG groups) had a larger dominant follicle than that of the control group (P=0.01). The percentage ovulating was highest in the PPG group (8 of 11, 73%), intermediate in the P group (4 of 13, 31%), and lowest in the control group (1 of 14, 7%; P<0.02). In Experiment 2, 16 heifers (14 to 16 mo old, 300 to 330 kg) were designated to have follicular wave emergence synchronized with either a CIDR and 1mg estradiol benzoate im (EP group, n=8) on Day 0 (beginning of experiment) or by transvaginal ultrasound-guided ablation of all follicles >or=5mm on Day 3 (FA group, n=8). On Day 7, CIDRs were removed in the EP group, and all heifers received 500 microg cloprostenol im. Ovulation was detected in 6 of 8 heifers (75%) in both groups. In summary, the use of PGF(2alpha) with or without exogenous progesterone treatment increased the percentage ovulating in heifers close to spontaneous puberty.