The erythema and wealing resulting from the application of thurfyl nicotinate ointment (Trafuril) and from the inoculation of kallikrein has been studied in patients with chronic urticaria and normal controls. Polyphloretin phosphate (PPP) suppressed the reaction in controls but in patients with urticaria it increased the reactions to Trafuril and had little effect on the kallikrein reaction. PPP also suppressed the PGE2-induced erythma in normal controls but not in urticaria patients. In a separate study using fibrinolysis autography, prostaglandin (PG) E2 and PGF2alpha depressed fibrinolysis in the skin of two pigs and both kallikrein and Trafuril suppressed fibrinolysis in human skin. It is suggested that the inflammatory reaction induced by thurfyl nicotinate and kallikrein is mediated in part by a prostaglandin-like action. Several anomalies in the action of Trafuril in skin diseases can be explained if such prostaglandin-like activity is mediated in part through inhibition of fibrinolysis.