Bradykinin (BK, 0.03-3.11 micrograms X kg-1 X min-1) was infused intravenously for 4-5.5 h to assess its effects on pulmonary transvascular fluid and protein exchange in three groups of artificially ventilated sheep prepared with lung lymph fistulas. In group I, BK was infused alone for 5.5 h. In group II, BK and captopril (SQ 14,225), an inhibitor of angiotensin-converting enzyme (ACE), were infused together because the effects of BK may be attenuated by its rapid degradation in the lung by ACE. In group III, BK was infused in the presence of propranolol, a beta-adrenergic antagonist, to prevent any permeability-decreasing effects of beta-adrenergic activation. The dosages of BK used, which decreased systemic arterial blood pressure by 10-20 mmHg, did not alter either pulmonary transvascular fluid and protein exchange or pulmonary hemodynamics at any time during infusion of BK alone or in combination with captopril or propranolol. Raising pulmonary microvascular pressure (Pmv) by inflating a left atrial balloon during the last 2 h of infusion in all three groups slightly increased pulmonary lymph flow and markedly decreased the lymph-to-plasma protein concentration ratio. These results are comparable with those obtained after increasing Pmv in normal anesthetized sheep and indicate that BK did not alter the pulmonary vascular permeability to proteins.