An analytical procedure is described for the determination of 1-(2-aminoethyl)-3-(2,6-dichlorophenyl) thiourea in dietary admix. Because of the complex nature of the carrier matrix, sample cleanup was required prior to HPLC separation. Sample cleanup was achieved using a cation-exchange microcolumn which yield highly reproducible results. HPLC separation was accomplished using a 10 mu C18 column, monitoring the column effluent in the ultraviolet region at 254 nm. After sample cleanup, 1-(2-aminoethyl)-3-(2,6-dichlorophenyl) thiourea could be detected at levels as low as 3 ppm in dietary admix.