The effect of an intravenous infusion of epinephrine or norepinephrine (45 microgram.kg-1.min-1) on the transcapillary exchange of fluid and protein were studied in anesthetized sheep prepared with lung lymph fistulas. After infusion of epinephrine, pulmonary lymph flow (Qlym) and the ratio of lymph to plasma protein concentration (L/P) did not change significantly from base line despite an increase in mean pulmonary arterial pressure (Ppa) from 17.3 +/- 0.8 to 22.6 +/- 0.09 Torr, In contrast, Qlym increased (p less than 0.05) from 9.24 +/- 1.53 to 11.46 +/- 1.97 ml/h and L/P decreased (p less than 0.05) from 0.78 +/- 0.03 to 0.74 +/- 0.04 after infusion of norepinephrine; these changes were associated with an increase in Ppa from 16.5 +/- 1.5 to 21.6 +/- 1.8 Torr. Pulmonary vascular resistance (PVR) increased from 5.90 +/- 0.83 to 12.12 +/- 1.23 Torr. 1-1 min (p less than 0-.01) after epinephrine and from 6.52 +/- 0.82 to 9.26 +/- 1.74 Torr.1-1 min (p less than 0.05) after norepinephrine. Left atrial hypertension, induced in four sheep infused with norepinephrine and in five sheep infused with epinephrine by inflating a left atrial balloon, increased Qlym and decreased L/P in all animals. Thus the infusions of epinephrine or norepinephrine did not increase lung vascular permeability to proteins. Epinephrine infusion also did not increase fluid filtration despite increases in Ppa and PVR, suggesting that pulmonary microvascular pressure did not increase significantly due to greater constriction of precapillary than postcapillary vessels. However, norepinephrine infusion increased filtration, suggesting that microvascular pressure was increased due to a greater constriction of postcapillary than precapillary vessels.