The study was designed to compare the efficacy of treatments intended to induce follicular wave synchronization among llamas (Experiment 1), and to determine the effect of these treatments on pregnancy rates after fixed-time natural mating (Experiment 2). In Experiment 1, llamas were treated with: (1) saline (control, n = 20); (2) estradiol and progesterone (E/P, n = 20); (3) LH (LH, n = 20); or (4) transvaginal ultrasound-guided follicle ablation (FA, n = 20). The ovarian response was monitored daily by transrectal ultrasonography. The intervals from treatment to follicular wave emergence and to the day on which the new dominant follicle reached ≥7 mm, respectively, did not differ between the LH (2.1 ± 0.3 days and 5.2 ± 0.5 days, respectively) and FA groups (2.3 ± 0.3 days and 5.0 ± 0.5 days), but both were shorter (P < 0.05) and less variable (P < 0.01) than in the control group (5.5 ± 1.0 days and 8.4 ± 2.0 days), while the E/P group (4.5 ± 0.8 days and 7.7 ± 0.5 days) was intermediate. In Experiment 2, llamas at unknown stages of follicular development were assigned randomly to control, E/P, and LH groups (n = 30 per group), A single, fixed-time natural mating was permitted 10-12 days after treatment. Ovulation rates did not differ among groups (control, 93%; E/P, 90%; LH, 90%; P = 0.99), but the pregnancy rate was higher (P < 0.05) for synchronized llamas (LH and E/P groups combined, 41/54) than for non-synchronized llamas (control group, 15/28). In conclusion, LH and FA treatments were most effective for inducing follicular wave synchronization, while E/P treatment was intermediate. Synchronization treatments did not influence ovulation rate subsequent to fixed-time natural mating, but a higher pregnancy rate in synchronized than non-synchronized llamas warrants critical evaluation of the effects of follicular status on the developmental competence of the contained oocyte. © 2003 Elsevier Inc. All rights reserved.