To determine whether checking serum chemistries is a useful procedure, records were reviewed to identify patients presenting to a university hospital emergency department (ED) with seizures. In a six-month period, 112 adult patients made 126 visits for evaluation and treatment of recent seizures. Analyzing each visit individually, 111 patients (88.1%) had serum electrolytes determined; 96 (76.2%) had a serum calcium level measured; and 92 (73%) had a serum magnesium level measured. The overall incidence of seizures due primarily to derangements in serum chemistry was 2.4%, including two hypoglycemic seizures and one seizure related to hemodialysis. Severe aberrations in serum chemistries occurred most frequently in alcoholics; nonalcoholics had relatively few abnormal test results unless they had preexisting renal failure or diabetes mellitus. In ED patients, the incidence of seizures due primarily to derangements in serum chemistry is very low. Grouping of patients by medical history can help direct test ordering by identifying those at risk for abnormalities in serum chemistry.