The presence of prostaglandins D2, E2, and F2 alpha was demonstrated and their contents measured in various regions of postmortem human brain, pineal body, and pituitary by using specific radioimmunoassays and gas chromatography-mass spectrometry. The three prostaglandins were widely distributed in similar concentrations ranging from several hundred pg/g wet weight to about 40 ng/g wet weight. Prostaglandins D2 and E2 showed consistent and similar regional distributions in all six brains tested; amounts were high in pineal body, pituitary, olfactory bulb, and hypothalamus. On the other hand, prostaglandin F2 alpha was distributed more evenly. Prostaglandin D synthetase and prostaglandin E synthetase activities were found in cerebrum homogenate from a single subject and were recovered from the 100,000 X g supernatant. The presence of 1 mM glutathione, reduced form, markedly stimulated the activity of prostaglandin E synthetase, but did not affect prostaglandin D synthetase activity. Activity of 15-hydroxyprostaglandin dehydrogenase was found in the cerebrum homogenate and was partially purified. This enzyme required NADP as a cofactor and copurified with prostaglandin E 9-ketoreductase.