The effect of various prostaglandins on hindlimb lymph flow and macromolecular transport was studied in dogs anesthetized with pentobarbital sodium. Lymph obtained by cannulating the popliteal lymphatics was collected at 30-min intervals and analyzed for protein and exogenously administered dextran (Dextran 110). Arterial blood was obtained at the midpoint of each collection period and similarly analyzed. Prostaglandins (E1, E2, F2alpha, and A2), the vehicle and histamine were injected subcutaneously into the paw of the dog. Prostaglandins slightly increased lymph flow (L') but the lymph-to-plasma concentration ratios (R) for total protein (T) and Dextran 110 (D) decreased. Permeability surface area products (PS) were not altered. The sieving ratios (RD/RT) were substantially less than 1 and were not altered by prostaglandins. These results indicate that selective permeability of the capillary is not impaired by prostaglandins. Timing sequences and dose-response relations were also completed for prostaglandins by subcutaneous testing in dogs injected with Evans blue (T-1824). Leakage of the T-1824-albumin complex occurred when large amounts (migrogram) of prostaglandins were administered, and the response appeared to be short lived (less than 30 min). While the prostaglandins possess vasoactive properties, as demonstrated by an increased lymph flow, they do not alter the restrictive transport of large molecules.