A 3-year-old female Greyhound presents difficulties of locomotion in the hind limbs after one round of the field since the beginning of the racing season. After making a diagnosis of relapsing rhabdomyolysis without secondary renal involvement, several blood samples were taken before and after the effort in order to determine the most adequate moment for clinical evaluation of a rise in serum enzymes. The possibility of making an early diagnosis and a attempt for prevention are discussed. Blood values in a population of racing Greyhounds are compared with data of the literature.