The kallikrein-kinin system has been thought to participate in the pathogenesis of anaphylaxis. Kallikrein, released from lungs, has been postulated to contribute to cardiovascular collapse. Further to test the hypothesis, we examined for the occurrence of a kallikrein-like enzyme in guinea pig lungs and examined for release of such an enzyme by isolated, perfused lungs of guinea pig sensitized to and challenged with egg albumin. In addition, we treated guinea pigs with the bradykinin potentiating agents, BPP9a and SQ 14,225. In parallel experiments, we examined for effects of non-steroidal anti-inflammatory agents on the supposition that prostaglandin-related substances may mediate or modulate actions of kinins during anaphylaxis. A plasma kallikrein-like enzyme was found in lung homogenates and occurred in concentrations greater than that of plasma itself. Similarly, a store of kininogen occurs in lungs. However, using a sensitive radioassay for kallikrein-like enzymes, we were unable to confirm that antigenic challenge of sensitized lungs causes the release of enzyme into pulmonary venous effluent. Further, we were unable to modify the acute course of anaphylaxis by pretreatment of guinea pigs with bradykinin potentiating agents. However, indomethacin and aspirin at 20-40 mg/kg were found to greatly increase the severity of pulmonary anaphylaxis in terms of increased resistance to ventilation and increased numbers of lung hemorrhages. Paradoxically, aspirin or sodium salicylate at 80-100 mg/kg prevents the characteristic rise of insufflation pressure and the formation of lung hemorrhages.