For induction of estrus from the respeat breeders and silent heat cows, 25 or 50 ㎎ of PGF₂α was intramuscularly injected and symptoms of estrus such as vaginal swollen, mucus state, existence of mounting and receptive standing conception rate and return intervals were observed. The results were as follows: 1. Eleven (78.5%) of 14 cows treated showed estrus and ten (90.9%) of the eleven observed estrus on day 3 after treatment. 2. Estrus was induced in five of the seven cows with silent heat and in six of the seven cows with repeat heat. 3. Ten cows in heat following the treatment showed the same vaginal redness and swollen cervix as those of natural heating cows. 4. A considerable amount of mucus in vigina was observed in the four cows. 5. Only three cows showed the sexual behavior of mounting and receptive standing during heat. 6. Three cows were conceived at the induced estrus and calved these after. 7. Four cows showed return intervals of 18-25 days. This investigation was supported by grant of PGF₂α from The Upjohn Company, Kalamz-zoo, Michican, U.S.A.. I sincerely thank Dr. S.H. Langford, Pacific region technical manager for his effort of granting PGF₂α and his deep consideration of this work.