The purpose of this study was to investigate sweat lactate, ammonia, and urea excretion in rugby players. Fifteen elite amateur rugby players volunteered to participate. The study was conducted during competitive matches in the official season. Plasma and sweat concentrations of lactate, ammonia, and urea were measured before and after the matches. Peak values for creatine kinase activity were observed 24 h after the match. There was no significant change between time points for blood lactate concentration but secretion rate per unit surface and time was significantly reduced after the match. Sweat ammonia concentration increased significantly during the match; values were significantly reduced after 24 h and still remained low at 72 h. Secretion rate was also reduced from 24 h. Urea concentration was significantly reduced at 48 h, while secretion rates decreased at 24 h and 48 h. Lactate in blood was significantly elevated during the match but not thereafter. Blood ammonia was significantly elevated during the match and did not differ from the resting values at 24 or 48 h. Urea in blood tended to decrease during the match, with a significant reduction at 24 h. Significant positive correlations were observed between blood and sweat concentrations for urea and ammonia but not for lactate. Sweat rate correlated positively with sweat lactate secretion. The fact that part of the ammonia formed during exercise is lost with sweat indicates the importance of the purine nucleotide cycle during rugby matches. Our data also confirm that sweat lactate concentration is not influenced by circulatory blood lactate in rugby players.