We documented normal pregnancy and the rate of pregnancy failure in female baboons by measuring chorionic gonadotropin (bCG) and progesterone (P) levels in 162 mated cycles of 70 baboon females on days 10, 12, and 14 postovulation. Females were mated with males during turgescene. The presence of pregnancy was defined by bCG levels >20 μg/ml by day 14 postovulation and/or documentation of a gestational sac using ultrasonography. Of the 162 cycles, 75 were fertile. Of these animals, 33 were used in other studies and thus were not included in these analyses. The analyses are based on 43 pregnancies from 91 cycles that were untreated throughout their gestations. Twenty-six of these pregnancies had abnormal bCG and/or progesterone levels in early pregnancy. All of those pregnancies with abnormal endocrine parameters terminated with spontaneous abortion (60%). Certain abnormal bCG patterns were repeatedly observed in some animals and were correlated with repeated spontaneous abortions. Of 17 pregnancies with normal bCG and P patterns, 15 (88%) continued to term with a normal fetal outcome. In this study, a pregnancy rate per mated cycle of 47% was observed, yet 60% of untreated pregnancies abortyed spontaneously. Overall 16% of the mated cycles had continuing pregnancies with normal outcome. These studies demonstrate that a high rate of early abortions occurs in the baboon and that a single bCG determination is insufficient to define the presence of a “normal” pregnancy which might be expected to carry to term with a normal outcome.