[en] One to 7 days after whole body exposure of mice to a single dose of 700 R of X-rays, little or no change was detected in prostaglandin-like activity in the brain, blood and seminal vesicles. Slight increases in intestinal and renal tissue were not significant. In the lung, mean activity rose from 62 ng/g to a transient peak of 145 ng/g wet weight on the fourth day (P < 0.05). In the spleen, mean levels rose steadily from 13.2 ng/g to 259 ng/g on the fourth day (P < 0.01), and were still 184.4 ng/g on the seventh day. Prostaglandin-like activity was measured 4 days after single doses of 200 to 700 R. In the lung, a significant rise was produced by 600 to 700 R, and in the spleen by 200 to 700 R. This layer chromatography showed that part of the prostaglandin-like activity in spleen extracts had an Rsub(F) similar to that of [³H]-prostaglandin E₁, and part to that of [³H]-prostaglandin Fsub(2a). Splenic tissue from mice exposed to 700 R four days earlier, inactivated prostaglandin E₁ less potently than did tissue from non-irradiated mice. (author)