1. 1. Granuloma was made by the subcutaneous injection of 2% carrageenin solution on the dorsum of male rats. Eight, 16, 24 and 72 h after the injection, the exudate from each rat granuloma was withdrawn and extracted for prostaglandins. 2. 2. Extracted prostaglandins were separated to prostaglandin E and prostaglandin F group by silicic acid mini-column chromatography. Then the amount of prostaglandin E and prostaglandin F 2α were determined by the radioimmunoassay method. 3. 3. The levels of prostaglandin E in the granuloma exudates were 4.6 ng/ml at 8 h after the carrageenin injection, then decreased to 3.6 ng/ml and to 1.1 ng/ml at 16 h and 24 h, respectively. Seventy-two h after the injection, prostaglandin E level was increased to 8.1 ng/ml. 4. 4. The levels of prostaglandin F 2α in the exudate were as follows: At 8 h after the carrageenin injection, the level was 9.4 ng/ml, then decreased to 1.3 ng/ml and to 0.8 ng/ml at 16 h and 24 h, respectively. Seventy-two h after the carrageenin injection, it was again elevated to 4.7 ng/ml. 5. 5. The exudate of granuloma, 24 and 72 h after the carrageenin injection, was incubated with [ 3H] prostaglandin e 1 at 37°C for 30 min. Then the acidic ether extract was subjected to reversed phase partition chromatography. It was found that the exudate of 24 h and 72 h granuloma had little activity of prostaglandin 15α-hydroxy dehydrogenase.