A method is described for the separation and estimation of 4-, 5-, 6-, and 7-hydroxyskatole sulfate esters in urine. After extraction from urine, the 5-, 6-, and 7-hydroxyskatole sulfate esters were hydrolyzed by a sulfatase preparation to the corresponding hydroxyskatoles. The 4-isomer was resistant to this enzymic hydrolysis. The hydroxyskatoles were then extracted by ethyl acetate from the hydrolyzate followed by extraction of the 4-sulfate ester byn-butanol. Each fraction was chromatographed on silica gel G thin layers, sprayed with a modified Ehrlich's reagent (p-N,N-bis(2-chloroethyl)aminobenzaldehyde), and the appropriate zones eluted from the chromatogram. The concentrations of each isomer originally present in the urine were estimated from the absorbances of the four eluates at their absorption maxima (ca. 600 mμ). The levels of the four isomeric skatolyl sulfates found in urines from 10 normal controls are given.