A reversed-phase high-performance liquid chromatographic system using a mobile phase of 0.05 M phosphoric acid--methanol (30:70) was developed for determination of iodochlorhydroxyquin (clioquinol, I) in biological material. I was extracted from samples with diethyl ether. Conjugates of I were hydrolyzed to free I and extracted by the same method. The ether phases were evaporated to dryness, reconstituted in the mobile phase and chromatographed using a microparticulate C18 column, a pre-column and a UV detector set at 256 nm. Quantitation of I in the range of 0.20-2.0 micrograms/ml of urine, 0.50-2.0 micrograms/g of liver, and 0.25-2.0 micrograms/g of feces was obtained with coefficients of variation of 0.02, 0.05, and 0.06, respectively. The detection limit of I was 0.2 micrograms. Extensive absorption of I upon topical application to dogs was also demonstrated.