Obese subjects are at increased risk for cardiovascular disease manifestations. The CK value is an important aid in the diagnosis of myocardial infarction, but may also be increased by factors such as muscle mass or breakdown of muscle tissue. We analysed CK values in 120 obese patients in our Obesity Unit and also monitored CK values during a weight reduction programme in 26 of these patients. CK values did not increase with body weight, and during weight loss in a diet programme no systematic CK changes were observed. We conclude that in the evaluation of an elevated CK value in a coronary care unit, such an increased value cannot be accounted for by the overweight per se.