alpha-Naphthyl isocyanate (NI) as a derivatizing agent to separate several beta-blockers was described. This procedure is simple, rapid and gives good resolution. Experiments with NI derivatives of alprenolol showed that the isocyanate group reacted with the amino group on the analyte to form urea under mild conditions and with the hydroxyl group to form carbamate under relatively vigorous conditions. The results also indicated that the derivatized reactions is 1:1 between NT and analytes.