We evaluate the mRNA expression of monocarboxylate transporters 1 and 4 (MCT1 and MCT4) in skeletal muscle (soleus, red and white gastrocnemius), heart and liver tissues in mice submitted to a single bout of swimming exercise at the maximal lactate steady state workload (MLSSw). After 72 hours of MLSS test, the animals were submitted to a swimming exercise session for 25 minutes at individual MLSSw. Tissues and muscle samples were obtained at rest (control, n=5), immediately (n=5), 5 hours (n=5) and 10 hours (n=5) after exercise for determination of the MCT1 and MCT4 mRNA expression (RT-PCR). The MCT1 mRNA expression in liver increased after 10 hours in relation to the control, immediate and 5 hours groups, but the MCT4 remained unchanged. The MCT1 mRNA expression in heart increased by 31 % after 10 hours when compared to immediate, but no differences were observed in relation to the control group. No significant differences were observed for red gastrocnemius in MCT1 and MCT4 mRNA expression. However, white gastrocnemius increased MCT1 mRNA expression immediately when compared to rest, 5 and 10 hours test groups. In soleus muscle, the MCT1 mRNA expression increased immediately, 5 and 10 hours after exercise when compared to the control. In relation to MCT4 mRNA expression, the soleus increased immediately and 10 hours after acute exercise when compared to the control group. The soleus, liver and heart were the main tissues that showed improved the MCT1 mRNA expression, indicating its important role in controlling MLSS concentration in mice.