Total creatine kinase and its isoenzymes CK-MB and CK-BB were measured in the serum of patients admitted with acute abdominal pain or signs suggestive of an intraabdominal catastrophe. Total creatine kinase was measured by automated spectrophotometry, CK-MB by chemiluminescent assay, and CK-BB by radioimmunoassay. Patients were grouped according to their final diagnosis: intestinal infarction (N = 8); all other diagnoses (N = 22); controls (N = 20). CK-BB in the infarction group (22.3 +/- 5.3 ng/ml, mean +/- SE) was significantly greater (P less than 0.01) than in the noninfarction or the control groups (11.0 +/- 0.8 ng/ml and 5.8 +/- 0.7 ng/ml, respectively). There were no differences in total creatine kinase and CK-MB in the three groups. Stepwise deletion multiple regression analysis of 26 independent regressors showed that among a cluster of six significant variables (R2 = 0.92, P less than 0.005), CK-BB greater than 20 ng/ml was the best predictor of intestinal infarction. Results of this study indicate that CK-BB isoenzyme measurement may be useful in the diagnosis of intestinal infarction in man.