We investigated the relationship between the pregnancy rate of bovine embryo transfer and collapsed protoplasm of epithelial cells in cervical mucus samples collected from 102 cows (Japanese Black, Holstein and their crossbred). The recipient cows were divided into 3 groups according to the proportion of collapsed protoplasm: group L, 20% or less; group M, 21 to 80%; and group H, 81% or more. Rates of pregnancy in these 3 groups were compared. The observation rates of collapsed protoplasma in cervical mucus were 28.4% (29 cows) in group L, 44.1% (45 cows) in group M and 27.5% (28 cows) in group H. The pregnancy rates following embryo transfer were 66.7% (14/21 cows) in group L, 51.4% (18/35 cows) in group M, and 33.3% (8/24 cows) in group H after eighty frozen embryo transfers. The group L and group M recipients had higher pregnancy rates after frozen embryo transfer than group H (P<0.05). The rate of pregnancy increased as the proportion of collapsed protoplasm decreased. There was no significant correlation between pH of mucus, proportion of collapsed protoplasma of epithlial cells and concentration of progesterone in plasma. The present results indicate that there is a relationship between rate of pregnancy and proportion of collapsed protoplasm in the cervical mucus. The high rate of pregnancy in cows with the low proportion of collapsed protoplasma in cervical mucus suggests that the proportion of collapsed protoplasm in cervical mucus is a reliable index for selection of cows for embryo transfer.