A biochemical marker of brain cell damage, the BB-isozyme of the intracellular enzyme Creatine Kinase (CK), was used to evaluate any possible injury to the brain, caused by an operation for a ruptured intracranial aneurysm (SAH). CSF-CK BB was assessed before and at intervals after operation in a series of 60 patients, aged 29-71 (mean 51 years) operated on for intracranial aneurysms, all but one after SAH. The m/f ratio was 18/42. 35 of the 60 patients were operated on acutely, i.e. within 72 hours after the SAH. CK BB was determined as CKB-activity after immunological inactivation of CKM. Normally there should be almost no detectable enzyme activity in the CSF. The pre-operative CK BB-activity was 0.01+ -0.01 mikrokatal in the patients in Hunt & Hess grade I who were operated on > 7 days after their SAH, and 0.05+ -0.04 in those operated on acutely, probably still reflecting the effects of the SAH on the brain. The mean per-operative CK BB increase was 0.11+ -0.17 for patients who had an uneventful postoperative course, compared to 0.39+ -0.49 for those showing some degree of immediate postoperative deterioration. This difference is significant at the 1% level. 52 of the 60 patients showed a rise of CK BB after operation. The mean increase for those patients operated upon in a good state and without any complication or postoperative deterioration was 0.02+ -0.03 mikrokatal, which could therefore be considered as a "normal" or acceptable elevation.(ABSTRACT TRUNCATED AT 250 WORDS)