• Acute brain damage—cerebrovascular or cardiovascular, traumatic or infectious—released brain-type isoenzyme of creatine kinase (BB-CK) into the circulation within a few hours in 16 of 62 patients (26%). Occurrence of BB-CK was transient in the serum. BB-CK activity was found in the peripheral blood in 13 of 23 patients with diffuse brain damage compared to three of 39 patients with a local cerebrovascular accident (P <.0005). The mortality of patients having BB-CK in their serum was 63% compared to 39% of those without BB-CK activity in their serum (P <.05).