Guinea pigs were sensitized with ovalbumin (100 mg i.p. and s.c.) 3 weeks before the lungs were removed and perfused free of blood with Tyrode solution (Brocklehurst, 1960 author, an asterisk (*) denotes the one who mepyramine (5 x 10-7 g/ml) and the remainder extracted with two volumes of diethyl ether at pH 3. The organic extracts were examined in various thin layer chromatographic systems using parent vrostaglandins (PGs) as standards.Six radio-labelled peaks were seen on scanning the TLC plates, two major and four minor. Two peaks had similar RF values to PGE2 and PGF2a and a minor peak had the same RF as arachidonate. The other peaks are as yet unidentified but probably include 13-14 dihydro PGE2 and 13-14 dihydro 15-keto PGE2 (Anggard and Samuelsson, 1965) and possibly similar metabolic products of PGF2o, Eicosatetraynoic acid (TYA, 10 jg/ml), a competitive inhibitor of PG synthesis, or disodium cromoglycate (10 jug/ml) were added to the closed circuit perfusion system 60 min after the [14CI -arachidonate, thus reducing the possibility that these compounds may interfere with uptake rather than PG synthesis. The lungs were then challenged and samples collected and processed as before. Each experiment was repeated at least three times and similar results were obtained on each occasion.TYA reduced all the radio-labelled peaks whilst cromoglycate had no effect.