The general morphology and direction of blood-flow in the renal portal complex, as well as the histochemistry, innervation and pharmacology of the renal portal valves were studied. The origin of the copious mucus present in the cloacal fluid was found to be in the collecting tubules and branches of the ureters. By simulating closed renal portal valve conditions in one of two groups of birds an attempt was made to study the role of the renal portal blood system. Significantly higher water diuresis was recorded in the "closed valve" group. Increased amounts of potassium were secreted by the "open vale" group while sodium was reabsorbed in significantly higher amounts in the "closed valve" group. No evidence to support the hypothesis that the renal portal system promotes renal tubular secretion of uric acid was found, but the high concentration of urea recorded and the trend for urea values to be higher in the ""closed valve"" group, suggests that the renal portal system may be implicated in urea secretion. Keywords: Acetylcholine, Adrenalin, Birds, Blood-flow, Cloacal fluid, Copious mucus, Glomerular filtration, Illustrations, Kidneys, Morphology, Nitrogen excretion, Osmoregulation, Penguin, Renal portal valves, Sodium chloride, Spheniscus, Tissue samples, Tubular secretion, Ureters, Uric acid, water diuresis.