The present study examined the effect of high-intensity exercise training on muscle sarcolemmal lactate/H+ transport and the monocarboxylate transporters (MCT1 and MCT4) as well as lactate and H+ release during intense exercise in humans. One-legged knee-extensor exercise training was performed for 8 wk, and biopsies were obtained from untrained and trained vastus lateralis muscle. The rate of lactate/H+ transport determined in sarcolemmal giant vesicles was 12% higher (P < 0.05) in the trained than in untrained muscle (n = 7). The content of MCT1 and MCT4 protein was also higher (76 and 32%, respectively; n = 4) in trained muscle. Release of lactate and H+ from the quadriceps muscle at the end of intense exhaustive knee-extensor exercise was similar in the trained and untrained leg, although the estimated muscle intracellular-to-interstitial gradients of lactate and H+ were lower (P < 0.05) in the trained than in the untrained muscle. The present data show that intense exercise training can increase lactate/H+ transport capacity in human skeletal muscle as well as improve the ability of the muscle to release lactate and H+ during contractions.