In a preliminary experiment, pigs fed a purified diet gained at the same rate as pigs fed a natural ingredient diet if the purified diet was formulated to provide 150% of the Na, K and Cl requirements. Subsequent experiments were designed to determine the interrelationships of dietary Na, K and Cl. Pigs were fed diets with Na (.03% to .60%), K (.1% to 1.0%) and Cl (.03% to .60%) levels arranged in a three-factor central composite design. Over the range of Na levels, predicted gain increased by .07 kg/d. Within this dietary range no interactions between Na and K or Na and Cl were observed, but changes in growth due to dietary K level were dependent on the dietary Cl level. Using canonical analysis of the response surface, a minimax of the observed K and Cl interaction was calculated to be .57% K and .27% Cl. An imbalance of dietary K and Cl was predicted to depress gain, and an increase in gain was predicted by a 1:1 addition of K and Cl above or below the minimax. The results of a third experiment failed to confirm that additions of K and Cl in a 1:1 ratio above the minimax altered gain (P greater than .10). Experiment 4 confirmed that an imbalance of K and Cl altered growth of pigs. At .1% K, an increase in dietary Cl from .03% to .57% depressed gain by .07 kg/d; at 1.1% K the same increase in dietary Cl improved gain by .16 kg/d (P less than .07). These results suggest that dietary K and Cl levels have an interactive effect on pig growth.