Introduction: To avoid injuries during high-intensity sports training, it is important to recognize conditions of bodily consumption and production of adequate energy; exercise increases the concentration of the blood lactate. This paper is an attempt to compare pre and post lactate tolerance exercise test -blood lactate concentrations -of elite boy swimmers. Methods: Blood lactates are measured by an enzymatic method on 12 subjects 30 minutes before and adjust and 24 hours after the test. Results: The mean lactate concentration of 30.35±12.16 mg/dl is observed in swimmers 30 minutes before the test. Swimmers adjust after the test show mean blood lactate concentration of 108.52±18.17 mg/dl that is significantly higher than 30 minutes before the test (p<0.001). Then blood lactate level decreases below baseline level at 24 hours after the test. Conclusion: Blood lactate increases with the test and decreases below baseline within 24 hours after the test.