To examine the blood metabolic responses of world-class boxers involved in international competition (Test match), 33 male boxers (mean ± SD) competing internationally across all the official weight categories were studied on 2 different occasions: Test match 1 (team A against team B) and Test match 2 (team A against team C). Blood samples were collected after the third round for both Test matches for all teams except team B. For all Test matches and boxers, mean blood lactate concentration ([BLac]), bicarbonate concentration, hemoglobin O2 saturation (SaO2), partial pressure for CO2 (PCO2), and pH were 13.6 ± 2.4 mmol·L(-1), 13.2 ± 2.3 mmol·L(-1), 95.0 ± 2.6%, 32.0 ± 5.5 mm Hg, and 7.22 ± 0.06 with 7/20 final pH values <7.20. The intermediate category (60-64 kg) was characterized by the greatest [BLac] (14.8 ± 2.9) compared with the heaviest and lighter boxers (∼12 mmol·L(-1)). During the second match (team A again team C), a significant difference between pH, PCO2, and SaO2 values was observed with no concomitant difference in [BLac] suggesting a better buffering capacity in team A. This result highlights the need for a well-developed anaerobic and buffering capacity and indicates that world-class boxers must be able to tolerate a substantial level of acidosis to produce high levels of boxing activity until the end of a match.