Effects of cadmium exposure on renal Na⁢ and K⁢ transports were studied in rats. During the course of cadmium treatment (2 mg Cd/kg/day, s.c. injections for 3 weeks) renal tubular transports of Na⁢ and K⁢ were evaluated by lithium clearance technique. During the early phase (first week) of cadmium treatment, urinary Na⁢ excretion decreased drastically and this was due to an increased Na⁢ reabsorption both in the proximal and distal nephrons. During the late phase (third week) of cadmium treatment, filtered Na⁢ load was decreased by reduction in GFR, but the renal Na⁢ excretion returned to the control level due to impaired Na⁢ transport in the proximal tubule. Urinary excretion of K⁢ did not change during the early phase, but it rose markedly during the late phase of cadmium treatment. These results indicate that a light cadmium intoxication induces a Na⁢ retention, and a heavy intoxication results in a K⁢ loss. Possible mechanisms for these changes are discussed.