Seven (41%) out of 17 subarachnoid haemorrhage patients had MB isoenzyme of creatine kinase (CK) in the serum. The peak activity of MB was observed about 16 h after the onset of neurological symptoms. Of the patients with MB activity, five (71%) had pathological ECG changes suggesting acute cardiac injury. Of the patients examined, five died, and four of these had both CK-MB and CK-BB isoenzymes in the serum. In a preliminary study a test was made whether MM and BB were converted to MB in 48 h at 4 degrees C or 20 degrees C in a saline solution containing mercaptoethanol and bovine serum albumin. Such conversion was not observed. Human brain tissue extract obtained at autopsy was used in the study.