The long-term responses of lymph flow, lymph protein transport, and the permeability-surface area (PS) product to hyperproteinemia have been studied in conscious dogs. Plasma protein concentration (PPC) was increased by daily intravenous infusion of previously collected autologous plasma for 9 days. Lymph flow was determined by collecting lymph chronically from a lymphatic afferent to the popliteal node in the hind leg. Compared with the average value during the normal-PPC period, the following changes occurred during 10 days of high PPC: lymph flow decreased from 12.3 ± 1.1 to 3.8 ± 0.6 µl/min, lymph protein transport decreased from 241 ± 24 to 141 ± 21 µg/min, PS product decreased from 4.7 ± 0.5 to 3.0 ± 0.5 µl/min, PPC increased from 7.1 ± 0.1 to 8.8 ± 0.4 g/dl, lymph protein concentration increased from 1.9 ± 0.1 to 3.8 ± 0.1 g/dl, plasma colloid osmotic pressure increased from 18.6 ± 0.8 to 24.2 ± 2.1 mmHg, and lymph colloid osmotic pressure increased from 4.8 ± 0.2 to 10.4 ± 0.7 mmHg. In conclusion, long-term hyperproteinemia in dogs resulted in chronic decreases in lymph flow, lymph protein transport, and the PS product and chronic increases in lymph protein concentration and lymph colloid osmotic pressure. The marked decrease in lymph flow during hyperproteinemia decreased lymph protein transport and thus contributed to the increase in lymph protein concentration. In addition, the decreases in PS product and lymph protein transport suggest that transcapillary protein flux decreases during hyperproteinemia.