The aim of the study was to determine the efficiency of adding sodium and chlorine to commercial cereal-soybean starter and grower diets with increased potassium content in broiler chickens raised under farm conditions. A total of 4800 day-old Hubbard Flex broilers were divided into 4 groups with 6 replicates 01200 chickens each and kept in boxes on straw litter. Basal starter and grower diets contained in 1 kg (as analysed): 8.37 and 8.27 g potassium; 1.79 and 1.66 g sodium; and 3.17 and 2.76 g chlorine, respectively. The dietary electrolyte balance (DEB) values were 203 and 206 mEq/kg, respectively. Basal experimental diets were supplemented with 0.3 g Na and/or 0.5 g Cl/kg of diet in the form of sodium carbonate, sodium chloride or ammonium chloride. The dietary supplements had no effect on production parameters during the starter period. In the grower period, the sodium (NaHCO3) supplement increased DEB value to 219 mEq/kg, significantly (P<0.05) increasing chickens' body weight gain and feed intake. Sodium added together with chloride as NaCl tended to improve production parameters (non-significantly) without any effect on DEB values. Throughout rearing, the positive effect of sodium supplementation was only observed for increased feed intake (P<0.05). Supplementation of chlorine (NH4Cl) to the starter and grower diets reduced DEB values to 188 and 192 mEq/kg, respectively, without a positive effect on rearing performance, and decreased feed intake (P<0.05). The analysed sodium and chlorine supplements had no effect on dressing percentage, abdominal fat content of the carcass and litter moisture.