The use of methylergonovine maleate and cloprostenol was tested during uterine involution in mares of different ages to determine whether these treatments could increase pregnancy rates. A total of 311 Thoroughbred mares from Southern Brazil that had experienced normal parturition and given birth to live foals was studied. After parturition, mares were submitted to clinical examination and, if necessary, to vulvoplasty. At that time, mares were randomly assigned to one of the following groups: GI-methylergonovine maleate (n = 77); Gil-cloprostenol (n = 82); GUI-control group (n = 152). Mares were mated every other day after a preovulatory follicle (> 40 mm) was detected. Pregnancy diagnosis was made on Days 18 and 42 postovulation. There were no significant differences in pregnancy rates among groups. Average number of days between parturition and ovulation was 11.8 ± 3.4 (GI), 13.2 ± 4.5 (Gil) and 13.2 ± 4.0 (GUI). There was no relationship between ovulation day and pregnancy rate, but a significant shortening of the parturition-ovulation interval was detected in GI (p < 0.05). Pregnancy rate of mares in GUI with ages less than 10 yr was significantly greater than that of older mares (p < 0.05). This difference was not detected in GI and Gil.