In eleven football players and in four football-reserve players urinary kallikrein and kininase activities were determined before and after an official match. The results showed a significant reduction of kallikrein after the match in football players when the football-reserve players were used for comparison (p less than 0.01). Kininase activity appears increased in football players after the match, but not significantly. The Kininase/Kallikrein ratio after the match resulted significantly increased in football players (p less than 0.05) and very significantly compared to the football-reserve players (p less than 0.01).