The aim of the 3 × 3 factorial experiment on broilers was to investigate the effect of high dietary levels of potassium (K) and different levels of sodium (Na) on chicken performance, carcass traits, dry matter content in excreta and nitrogen balance. Three hundred and sixty one-day-old Ross 308 chickens were allocated to 9 groups, in 5 replicates of 8 (4♂ and 4♀). Chickens from 1 to 42 days old were kept in cages with wire floors to enable excreta collection, and were provided with water and feed ad libitum. The basal starter (days 1-14) and grower (days15-42) diets contained, as analysed, 1.73 g and 1.89 g·kg^-1 chloride (Cl), 10.7 g and 10.8 g K and 0.69 and 0.94 g Na, respectively. Basal diets were supplemented with cations containing, as analysed, 12.2/11.8 g and 12.7/12.5 g·kg^-1 K and 1.22/1.25 g and 1.68/1.61 g·kg^-1 Na, for the starter/grower periods of feeding, respectively. The molar proportion of Na:K in diets used in the experiment ranged from 0.09 to 0.27 in the starter diet and from 0.13 to 0.25 in the grower/finisher diet; the dietary electrolyte balance (DEB) values varied between 255 to 349 and 264 to 336, respectively. During the starter feeding period, body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR) in the chickens were positively affected by increasing the Na supplement. Throughout the feeding period, Na supplementation improved BWG, FI and FCR and production index values and increased carcass yield. The dry matter content of the excreta was negatively affected by the K level in the diet; the 12.7 g K dietary content, in particular, caused a higher moisture content.