A high-performance liquid chromatographic method is used for the determination of citalopram [1-(3-dimethylaminopropyl)-1-(4-fluorophenyl)-5-phthalancarbonitrile+ ++] and four of its metabolites (the methylamino, amino, propionic acid and N-oxide derivatives) in plasma and urine. The plasma samples were extracted with diethyl ether at pH 10 and pH 4. Filtered urine samples could be injected directly on to the column. Steady-state drug and metabolite levels were investigated in fifteen psychiatric patients. In urine, 12 +/- 5% (mean +/- S.D.) of a given dose of citalopram was excreted in unchanged form. The propionic acid derivative was further conjugated, possibly to glucuronic acid. Mean steady-state plasma levels and metabolites in 24-h urine are given as percentages of the dose.