The performance and the physiological and metabolic consequences of three dietary levels of Na (.03, .09 and .18%) and of Cl (.08, .17 and .32%) arranged factorially were determined in growing-finishing pigs (36 to 89 kg). Average daily gain and feed efficiency of pigs fed .03% Na were lower than pigs fed .09 or .18% Na. Gain:feed ratio of pigs fed .32 or .17% Cl was greater than that of pigs fed .08% Cl during the finishing phase (58 to 89 kg) but not during the growing phase. Increasing dietary Cl levels increased average daily feed intake and gain:feed ratio of pigs fed .03% Na, but had no effect at the higher levels of Na. Plasma Na and Cl were lower (P less than .05) while plasma K (P less than .01), total protein, (P less than .04), albumin (P less than .07) and urea N (P less than .03) were higher in pigs fed .03% Na compared with those fed .09 or .18% Na. Increasing the dietary levels of Cl decreased urea N (P less than .05). Plasma lysine:arginine ratio increased as dietary Cl increased in pigs fed .18% Na diets, but not in pigs fed .03 or .09% Na. The urea cycle intermediate ornithine was highest in the plasma of pigs fed .18% Na. Dietary Na and Cl seem to interact to affect both plasma electrolytes and basic amino acid metabolism.