BACKGROUND Exercise induces renal hemodynamic alterations and stimulates electrolytes excretion. The purpose of this study was to assess urinary excretion of sodium and potassium in karate practitioners, following competitions. METHODS The study population composed of 18 healthy men, aged 18 to 21 years, with similar physical characteristics. They were professional karatekas with a history of at least 7 years of karate training. The participants competed in 3 rounds of about 3 minutes in duration with 10 minutes resting intervals between them. The 24-hour urine samples were collected before (while trainings were stopped) and after the match and their sodium and potassium concentrations were measured. Also, blood samples were obtained before and after the match for measurement of these electrolytes in the participants' sera. RESULTS Before the match, the mean values of urinary sodium and potassium were 200.3 +/- 89.3 mEq/L/d and 68.5 +/- 12.9 mEq/L/d, respectively. After the match, they changed into 206.9 +/- 74.7 mEq/L/d and 67.1 +/- 14.4 mEq/L/d, respectively. No significant alterations were observed in urinary sodium and potassium excretion following karate match (P = .94 and P = .96, respectively). Serum sodium levels were 136.7 +/- 3.1 mEq/L and 136.3 +/- 2.9 mEq/L, before and after the match, respectively (P = .11), serum potassium levels were 4.2 +/- 0.3 mEq/L and 4.1 +/- 0.2 mEq/L, respectively (P = .16). CONCLUSIONS With regard to short duration and anaerobic nature of karate, it seems that a Karate match does not contribute to excessive urinary electrolytes excretion.