The enzymatic activity of creatine kinase-MB isoenzyme (CK-MB), a sensitive and specific marker of myocardial damage, was measured in 32 children following scorpion envenomation. CK-MB activity, total creatine phosphokinase (CPK) and serum glutamine oxalacetic transaminase (SGOT) levels were examined for relationship with electrocardiographic (ECG) results and the clinical state of the children. Twenty-seven out of the 32 children had signs of systemic intoxication ("symptomatic" cases), while the other five children had only local signs ("asymptomatic" cases). Thirteen out of the 27 symptomatic children had enzymatic myocardial involvement characterized by high total CPK level, elevated CK-MB level and a CK-MB/CPK ratio exceeding 6%. Six of these 13 children had ECG changes consistent with myocardial damage, and only one child had clinical signs of myocardial injury. None of the asymptomatic children, nor five healthy control children, had any evidence of myocardial damage as judged by CK-MB levels, clinical signs and ECG. Our study suggests that CK-MB activity is specific and highly sensitive in detecting myocardial damage in children following scorpion envenomation, and appears superior to ECG and clinical parameters. We speculate that the myocardial lesions are too small to cause heart failure in most cases, but they may account for the cardiovascular changes frequently seen in scorpion envenomation.