Brain-type creatine kinase (CK) isoenzyme (CK-BB) was detected in the serum in 13 out of 26 patients with acute brain injury (50%). The peak of CK-BB activity ranged from 5 to 188 U/liter, constituting, on average, 10.5% of the total CK activity. The highest activities were seen in patients with gunshot wounds. High CK-BB activity was associated with poor prognosis, but minimal CK-BB elevations did not have prognostic significance. Heart-type creatine kinase isoenzyme (CK-MB) was detected in the serum in 17 out of 26 patients (65%). The peak activity ranged from 5 to 115 U/liter, constituting, on average, 6.6% of total CK activity. Electrocardiogram taken from 20 patients revealed transient T-wave inversions in the precordial leads in four patients; three of them also showed serum CK-MB activity. Subendocardial hemorrhage was detected at autopsy in three of the five CK-MB-positive patients, but in none of the four CK-MB-negative cases. Present findings suggest that acute brain injury may be secondarily cause myocardial damage.