1. One-day-old male broiler chicks were fed on diets containing 3-8% or 2-7% added NaCl in two experiments lasting 22 and 42 d respectively. 2. Sodium clearance was increased in treated birds in both experiments. No other changes in renal function were observed but an increase in plasma urate in treated birds of the first experiment may indicate some loss of proximal tubular function. 3. Renal function, relative to body weight, diminished slowly with age in control and treated birds but these changes could not be related to the fact that at about 3 weeks of age testicular cysts no longer develop.