Isolation from carrageenin-induced granuloma of rat of factors affecting phospholipase A2 (PLase A2) activity was attempted. Excised granuloma was extracted with 2% phenol and denatured both at acidic and alkaline pH's in boiling water. The extract was adsorbed on charcoal and eluted in an alkaline milieu. Following gel chromatography of the eluate on Sephadex G-25, the effect of this fraction on PLase A2 prepared from rabbit peritoneal exudates was examined. Materials affecting PLase A2 activity were eluted slightly behind the peak of saccharides having an approximate molecular weight of 800. Activation of PLase A2 was most pronouncedly observed in the sample prepared from 5 days granuloma. Activating effect on PLase A2 was not observed with the sample prepared from control rat skin. The effect of fractions that contained PLase A2 activating components on vascular permeability was investigated by measuring the leakage of i.v. administered pontamine blue. Injection of the sample containing PLase A2-activating materials into mouse paw induced the increase of vascular permeability in a dose dependent manner. Maximal effect was observed also in the sample obtained 5 days after the injection of carrageenin. Thus, the activating components may be involved in the processes of inflammation.