An original method for the collection of pure or nearly pure pulmonary lymph in the canine is desirable for the study of pulmonary water, protein dynamics and cells. Right lymphatic duct lymph has been used extensively but it known to contain lymph from a number of extrapulmonary sources and has been altered by passage through lymph nodes. Pulmonary lymph was collected from 13 dogs through an open chest. The mean flow of lymph was 1.5 milliliters per hour +/- 0.08. This flow is compared with 3.7 milliliters per hour from the right lymphatic duct and 22.5 milliliters per hour from the thoracic duct in a group of dogs with a closed chest. The levels of lactate dehydrogenase--634 units per liter--and glutamic-oxalacetic transaminase--416 units per liter--in pure pulmonary lymph were much higher than in right lymphatic duct lymph--lactate dehydrogenase 125 units per liter; glutamic-oxalacetic transaminase 94.0 units per liter, in thoracic duct lymph--lactate dehydrogenase 47 units per liter; glutamic-oxalacetic transaminase 80.5 units per liter--and in blood plasma--lactate dehydrogenase 299 units per liter; glutamic-oxalacetic transaminase 95 units per liter. Low levels were noted in Na+, 107, and Cl-, 85, in pure pulmonary lymph versus plasma--Na+ 145; Cl- 112, right lymphatic duct lymph--Na+ 146; Cl- 115, and thoracic duct lymph--Na+ 146; Cl- 114. The method can be adapted for prolonged drainage in conscious dogs, which would enhance its usefulness.