Seizure is a common problem evaluated in pediatric emergency departments. Serum chemistry analysis is often performed as a routine part of the diagnostic evaluation of children who arrive in the ED with seizure. From this retrospective study, we sought to determine 1) how often serum electrolytes (Na, K, Cl, CO2), total calcium, magnesium, ammonia, and glucose chemistries were performed, 2) the frequency of abnormalities detected, and 3) whether abnormalities resulted in a change in patient care. Three hundred eight ED charts from 12 consecutive months were reviewed. Data collected included age, sex, ED diagnosis, medical history, and physical examination. Charts were also reviewed for diagnostic tests ordered and patient management. Children were classified as having febrile (FS) or nonfebrile seizures (NFS) to establish diagnostic evaluation practices for each group as well as to determine rates of laboratory abnormalities. Three hundred eight children were enrolled, 108 (35%) FS and 200 (65%) NFS. The mean ages of FS and NFS patients were 2.1 and 5.7 years, respectively (P less than 0.05, t-test). One hundred twenty-four of 308 (40%) children had at least one test performed; no abnormal test was thought to have caused seizure; none was treated. One hundred five of 308 (34%) were experiencing their first seizure. There was no difference in the likelihood of having a test ordered for children with a first seizure, regardless of seizure category. We concluded that 1) abnormal serum electrolytes, total calcium, magnesium, and glucose rarely cause seizure in children and 2) routine use of these tests in the ED is costly and does not contribute to seizure therapy.