Because estrogen may be involved in maternal recognition of pregnancy and embryonic migration in llamas, expression of estrogen receptor subtypes α (ERα) and β (ERβ) was evaluated in corpus luteum (CL), endometrium, and uterus using relative RT-PCR. Tissues were recovered from sterile-mated (SM) and pregnant (PG) females during Days 7–11 and 7–13 (Day 0 = day of mating), respectively, and follicular phase and juvenile females. Luteal expression of ERα and β was similar (P > 0.10) in SM and PG females and within Days 7–11, however, expression of ERα in ovarian tissue from follicular phase females was greater (P < 0.05) than Days 7 and 9 CL. Uterus expressed less ERα and β compared to endometrium (P = 0.07 and P < 0.01, respectively). Expression of ERα was greater (P < 0.05) in Day 7 and follicular phase uteri than Days 9 and 11, Day 13 PG and juvenile uteri. Uterine ERβ expression was greater (P = 0.09) in PG versus SM females and in mated compared to follicular phase females (P < 0.05). Endometrial expression of ERα and β did not differ (P > 0.10) between SM and PG females or by day. The presence of luteal ER during this period may mean a role for estradiol in maternal recognition of pregnancy. Observed increases in uterine ER expression with no changes in endometrium suggest expression increased in myometrium and/or perimetrium. Upregulation of myometrial ERβ in PG females may be involved in supporting uterine migration of the embryo. Mol. Reprod. Dev. 74: 1043–1052, 2007. © 2007 Wiley-Liss, Inc.