The serum ionized calcium, phosphate parathyroid hormone, and myoglobin levels were observed in a patient with idiopathic hypoparathyroidism and rhabdomyolysis. Since calcium levels best correlate inversely with serum myoglobin and lactic dehydrogenase, we suggest that these two enzymes are better markers of the activity of rhabdomyolysis than serum creatine phosphokinase or SGOT. Furthermore, a non-hormonal, nonrenal mechanism is important in the fluxes of serum calcium and phosphate in rhabdomyolysis.