We review some of the effects that insulin exerts on glomerular and tubular functions. In healthy subjects, insulin has little or no effect on renal hemodynamics, glomerular filtration rate, or permeability to albumin. In patients with noninsulin-dependent diabetes, hyperinsulinemia selectively increases urinary albumin excretion. In vivo, euglycemic hyperinsulinemia is associated with reduced urinary sodium excretion both under conditions of forced and normal diuresis. Whether the principal site of this action is the proximal or distal tubule remains somewhat controversial. The effect, however, is not mediated by insulin-induced hypokalemia and antikaliuresis, as it is still observed when plasma potassium concentrations and urinary potassium excretion are maintained. Hyperglycemia potentiates insulin antinatriuresis through an effect on the proximal tubule (sodium-glucose cotransport). Insulin antinatriuresis is accompanied by a reduction in the urinary excretion of uric acid. Both the antinatriuretic and antiuricosuric effect of insulin are preserved in states of insulin resistance of glucose metabolism (obesity, diabetes, essential hypertension). Thus, in insulin resistant individuals compensatory hyperinsulinemia imposes a chronic antinatriuretic and antiuricosuric pressure on the kidney. This may provide an explantation for the clustering of insulin resistance with hypertension and hyperuricemia.