A small number of investigators, including our team, has been responsible during the past two decades for many studies focusing on the kidney lymphatics. Interesting new information and concepts have been published, but unfortunately some of these data are scattered in obscure journals. The major purpose of this, and three subsequent reviews, is to present these new concepts in a more organized fashion. The reviews will also allow our group an opportunity to emphasize physiologic principles which have been ignored in the past. In a future review we will emphasize the role of the immunoblast, found only in kidney lymph and responsible for rejecting the renal allograft. Azathioprine (Imuran), if given early and in adequate dosage, will reduce the role of these transformed lymphocytes. Still another review article will emphasize the importance of renal tissue concentrations of antibacteria in eradicating acute pyelonephritis. Blood and urine levels of antibiotics are also important in eradicating pyelonephritis. Since renal lymph represents interstitial fluid, the concentration of appropriate bacteria-sensitive antibacterials is probably more important. We have now evaluated fourteen antibacterials individually in the mongrel dog, comparing plasma, urine, and renal lymph levels during similar time intervals. Finally, we will review the role of diuretics in altering the interstitial gradient of various solutes. Osmotic diuretics of more potent diuretics which affect renal tubular reabsorption manifest their action by different means when renal lymph fluid is evaluated.