The measurement of carbamazepine (CBZ) in samples from the emergency room (ER) raises several issues for drug monitoring. First, the ER frequently requires rapid turnaround time for clinical samples; this need may be more conveniently met by automated immunoassays than by high-performance liquid chromatography (HPLC), the other major analytical technique for measurement of carbamazepine. On the other hand, immunoassays often do not completely measure the pharmacologically active carbamazepine epoxide metabolite and therefore may not indicate the full extent of serum anticonvulsant activity. Second, patients may be admitted to the ER specifically because of seizure activity, which may be an indication of under- or overmedication with carbamazepine and which, if due in large part to high levels of the epoxide metabolite, may not be fully assessed by immunoassay. We examined the results of carbamazepine determination in 102 consecutive samples sent from an ER. Each sample was analyzed by a fluorescence polarization immunoassay (FPIA) and by HPLC. There were good correlations between the FPIA and the HPLC for the parent drug and for the sum of the parent drug plus metabolite (carbamazepine-10,11-epoxide, CBZ-E) with these regression equations: FPIA = 1.13 (HPLC CBZ) + 0.09 (r2 = 0.93) and FPIA = 0.93 (HPLC CBZ+CBZ-E)-0.55 (r2 = 0.89), respectively. There were weak correlations between the FPIA and the epoxide and between the parent drug and the epoxide. Based on the FPIA and HPLC results, we classified each value relative to the therapeutic range, i.e., supratherapeutic, subtherapeutic, or therapeutic.(ABSTRACT TRUNCATED AT 250 WORDS)