Abstract: The effect of treatment with natural and synthetic progesterone and estradiol on pregnancy rate in anestrous and lactating Bos taurus x Bos indicus crossbred cows with low body condition in a tropical environment was determined. On day 0, 107 anestrous cows were assigned randomly to five treatments; CIDR+ECP+P4 (n = 24), 1.9 g natural progesterone contained in a vaginal insert (CIDR), left 9 days in situ + i.m. 2 mg Estradiol Cypionate (ECP) and 100 mg synthetic Progesterone (P4); CIDR+ECP (n = 22): CIDR + i.m. 2 mg ECP; CIDR+EB+P4 (n = 20), CIDR + i.m. 10 mg Estradiol Benzoate (EB) and 100 mg P4; CIDR+EB (n = 21), CIDR + i.m. 10 mg EB and control (n = 20) i.m. 5 mL saline solution. The CIDR-treated cows received artificial insemination 48-56 h after CIDR removal and the control cows at 12 h after detected estrus. Pregnancy rate was 20.8% for CIDR+ECP+P4, 22.7% for CIDR+ECP, 10% for CIDR+EB+P4, 9.5% for CIDR+EB and 0% for the control group (p>0.05). Treatments used in this study resulted in similar pregnancy rates in anestrous Bos taurus x Bos indicus crossbred cows with low body condition.