The kinetics of oxidation of L-arginine and L-histidine by chlora­mine-T in alkaline media showed a first-order dependence of the rate on both chloramine-T and amino-acid concentrations, with no effect of change in ionic strength. The rate of reaction decreases as the pH is increased over the range 10 to 12. The energies of activation were found to be 65.3 and 51.8 kJ mol , and the entropies of activation -84.7 and -124.6 J K mol ,for arginine and histidine respectively. The effect of solvent has also been studied, and evidence is presented that the main mechanism of reaction is by interaction of the anion of the amino acid with the RNHCl species of chlora­mi ne- 1. The fract i ona 1 order of react i on wi th respect to [OH -] is probably due to involvement of OC1-, which is present in low concentration.