During 1937-1947, research into Renal Disease centered on the hypertension–kidney injury nexus, with robust links established between arterial hypertension and unilateral renal disease and hypertensive nephropathy. Experimental nephritis models and renal physiology studies illuminated mechanisms of kidney injury, reserve, and functional adaptation, while investigations into glomerulonephritis elucidated prognosis across ages. Developmental and congenital renal anomalies were described as distinct renal-phenotype patterns, expanding the spectrum of renal pathology seen in this era. Historical Significance: The immune-mediated nephritis model in rats provided a controlled platform for studying glomerulonephritis progression and testing therapies, setting a lasting template for nephrology research. Demonstrations that unilateral renal disease can drive systemic hypertension revealed early renal regulation of blood pressure and influenced subsequent management of renovascular and hypertensive renal disease. Foundational physiological measurements of urea excretion and nephron mass effects established baselines for diagnosis, monitoring, and surgical planning, while the elucidation of malignant hypertension’s cardiovascular–renal changes shaped the conceptual framework for hypertensive renal disease and guided future mechanistic research.