These experiments were conducted to investigate the effects of PGF₂α injection on induction of estrus and change in blood progesterone concentration in normal and anestrous gilts. Six anestrous gilts and 5 normal gilts were used. For induction of estrus either 10㎎ PGF₂α or 10㎎ PGF₂α plus 1,000IU PMSG was intramuscularly injected. Serum progesterone concentration were determined by radioimmunoassay. Conception of gilts were confirmed by necropsy examination for ovary and uterus condition within 35 days after mating. The number of gilts which showed standing or dull estrus after either PGF₂α or PGF₂α plus PMSG injection was 5(83.3%) out of 6 long-anestrous gills and 4(80.0%) out of 5 normal gills. The average interval from PGF₂α injection to the induced estrus was 7.2 days (4 to 12 days) in 5 long-anestrous gills and 13.5 days (6 to 25 days) in 4 normal gills. The number of pregnant gills was 2 out of 4 long-anestrous gills and 3 out of 4 normal gills, except each one get in two groups which was necropsied too early to be confirmed whether pregnant or not, although their ovary and uterus were normal condition. Blood progesterone concentration of 11.0 ng/㎖ before PGF₂α injection in 5 longanestrous gills which showed estrus decreased to 3.0 ng/㎖ at 1 day and 1.3 ng/㎖ (11.8% of initial concentration) at 4 days and increased again to 4.3 ng/㎖ at 8 days after PGF₂α injection, respectively and the concentration of 16.5 ng/㎖ before PGF₂α injection in 4 normal gills which showed estrus decreased to 3.2 ng/㎖ at 1 day and 2.3 ng/㎖ (13.9% of initial concentration) at 4 days and increased to 4.7 ng/㎖ after PGF₂α injection, respectively. Blood progesterone concentrations at 10 to 15 days and 30 to 35 days after mating in pregnant gills were 8.2 to 26.4 ng/㎖ and 17.7 to 19.6 ng/㎖ in 2 anestrous gills and 23.1 to 28.5 and 19.6 to 19.9 ng/㎖ in 3 normal gills respectively. The number of corpus luteum in the induced estrous gifts averaged 18.8 in 3 longanestrous gifts and 15.0 in 4 normal gifts. There would appear to be larger number of CL in PGF₂α plus PMSG injection than in only PGF₂α injection.