A high-performance liquid chromatographic method was developed to estimate the amount of taurine in tissue extracts and body fluids. Shodex Ionpak C-8 11, an adsorption-distribution type column, was chosen and combined with 3 mM perchloric acid as the mobile phase. The eluted taurine was derivatized with o-phthalaldehyde-2-mercaptoethanol reagent and measured at an absorbance of 350 nm instead of fluorescent intensity. Using this method, it was possible to isolate and estimate the amount of taurine from other coexisting substances or structural analogs such as hypotaurine, cysteamine, or cysteinesulfinic acid. For rapid routine assays of taut-me in many biological samples, it is advisable that the tissue extracts be pretreated with cation-exchange resin to exclude other interfering substances including 0-phosphoserine. The linear relationship between the concentration of taurine and absorbance achieved over the concentration range 0. I -10.0 nmol and the recoveries obtained were 98-10 I % by the internal standard method. The specificity, reproducibility, and sensitivity of this method for taurine were good enough to be used for biological applications. Examples of the tissue levels of taurine in various organs of the rat, as determined by this new method, are also presented. o 1987 Academic Press, Inc.