The purpose of this experiment was to investigate the effects of adrenalectomy and PMSG treatment on reproductive organs and serum steroid hormone level in immature female rats. The animals used in this experiment were 25 days old female rats weighing a, pp.oximately 70g. They were randomly divided into two groups of intact rat group (Int-) and adrenalectomized rat group (Adx-) and each group were subdivided into two groups of Non-PMSG (-Cont) and PMSG treated (-PMSG) group. The rat of PMSG-treated group (-PMSG) was administered subcutaneously with 25 IU PMSG on first day (9 a.m.) after adrenalectomy. The adrenalectomized rat groups were su, pp.ied with saline solution through the experiment period. The rate of ovulation and vaginal opening and reproductive organ weights were observed at 8, 32, 56, 80 and 104 hours after PMSG treatment. At the same time, the serum level of estradiol-17${eta}$ and progesterone were measured by the radioimmunoassay. The results obtained were as follows: 1. Ovulation was shown at 56 hours after treatment in Int-PMSG group and Adx-PMSG group and Adx-PMSG group. The rate of ovulation was very low in PMSG-treated groups, but it was increased in 80 to 90% at 104 hours after treatment. However, there was no ovulation in Int-Cont group and Adx-Cont group. 2. Vaginal opening was shown at 56 hours after treatment in Int-PMSG group and Adx-PMSG group and a, pp.ared in 80% at 104 hours after treatment. The rate of vaginal opening in PMSG-treated groups was very low, but Int-Cont group and Adx-Cont group had no vaginal opening. 3. The weight of ovary and uterus in two PMSG-treated groups were increased with the elapse of time after treatment and were significantly heavy in all observation time, but changes in Int-Cont group and Adx-Cont group were not recognized. The weights of ovaries and utera in Adx-Cont group were increased with the elapse of time. 4. The level of serum estradiol-17${eta}$ was remarkably increased in PMSG-treated groups (Int-PMSG and Adx-PMSG groups) compared with Int-Cont and Adx-Cont group, and significant difference was recognized between Non-PMSG group and PMSG-treated group in the experimental period. Especially, the highest levels of Int-PMSG groups and Adx-PMSG groups were shown at 80 and 56 hours after treatment and after ward estradiol-17${eta}$ levels of PMSG-treated groups were decreased. However, changes of the levels did not a, pp.ared in Non-PMSG groups at 104 hours after treatment. 5. The level of serum progesterone in PMSG-treated groups was significantly increased between 80 and 104 hours after treatment. With the elapse of time, the level was increased in all observed groups except for Int-Cont and Adx-Conx group. And the order from the highest level at 104 hours after treatment was Int-PMSG, Adx-PMSG, Int-Cont and Adx-Cont group.