The present investigation has been undertaken to understand the mechanism of mammalian implantation process, by demonstrating the role of ovarian steroids in the differentitation of the reproductive organs.

Attempt was made to examine the activity of alkaline phosphatase(ALP) in the oviduct, antimesometrium and the mesometrium of the uterine on Day 3 and Day 6.

1) The difference of the activity in the oviduct was not founded on Day 3 and Day 6.

2) The effect of estradiol on the differentiation of the oviduct was appeared on Day 3.

3) The difference of differentiation was not founded in the animesometrium and the mesometrium on Day 3.

4) The activity of ALP in the antimesometrium was higher than that in the mesometrium on Day 6.

5) The activity of ALP in antimesometrium on Day 6 was significantly higher than that observed on Day 3.

6) The effect of ovarian steroid homones on the differentiation of the uterine endometrium on Day 6 was obviously higher than that on Day 3. In particular, the effect of progesterone was markdly observed on Day 6.

This study, therefore, clearly demonstractes that estradiol is effective the differentiation of the oviduct preparing implantiation, but progesterone has much potent in the antimesometrium differentiation at the immplantation period.