The sweat gland has some similarity with the convoluted tubules of the kidney. Little is known about sweat secretion and electrolyte content of sweat in the uremic gland. A pilocarpine ionotophoresis sweat test was performed in 40 patients with advanced renal failure (RF). Sweat secretion was measured and analyzed for Na, K, and Cl and correlated to blood parameters, type, and duration of dialysis. The sweat weight was significantly lower in all RF patients when compared with this parameter in healthy controls (p < 0.0001). No difference was noted between patients undergoing hemodialysis, those undergoing continuous ambulatory peritoneal dialysis, and those not undergoing dialysis. Men sweated more than women among RF patients and among controls (p < 0.0001). An inverse correlation was found between sweat weight and blood calcium levels (p < 0.001). Sweat K concentration was significantly higher (p < 0.0001) in patients with RF than in healthy controls, while the concentrations of Na and Cl were similar. Several mechanisms are suggested as possible explanations for these changes.