A sensitive spectrofluorimetric method is described to determine small quantities of prostaglandin E2 in complex biological systems as intestinal tissues. The method is based on a solid phase extraction combined with a coupling with a fluorescent marker and measuring the derivatization product by fluorescence densitometry. After mixing the tissue with an ice-cold perchloric acid solution, adjusting the pH, centrifugation and filtration steps, the prostaglandins are retained on a solid phase extraction C18 disposable column. They are eluted with diethylether, derivatized with 4-bromomethyl-7-methoxy-coumarin using potassium carbonate as condensating agent and finally analysed using fluorescence densitometry on silica gel TLC plates. Applying this method, amounts down to 5 ng (per gram wet tissue) could be measured in intestinal tissues, the s.e.m. for replicated total analysis being less than 15%. The foregoing method is applied for the determination of PGE2 released in the intestinal wall under the influence of laxatives.