AbstractA patient with recurrent attacks of exertional rhabdomyolysis and easy fatiguability was treated with dantrolene sodium. She experienced a complete prevention of myoglobinuric attacks and gained a better exercise tolerance. Biochemical findings in this patient suggest a loosely coupled oxidative phosphorylation in mitochondria. The question is raised as to whether dantrolene sodium exerts an effect on the mitochondrial calcium uptake and influences the state of coupling of the mitochondria.