Serum creatine phosphokinase(CPK) levels were measured serially in 20 adults with closed tibial shaft fractures, CPK activity increased significantly after fracture(p<0.01). High energy and delayed healing fractures had significantly higher levels of CPK than low energy and normally healing fractures, respectively. Thus, CPK determinations could be used to assess the severity of trauma and possible prognosis of the healing in tibial shaft fractures.