The rate of chlorination by molecular chlorine of 2-chloroacetanilide in acetic acid has been measured at 25°. Analysis of the products by isotopic dilution gave 85% of the 2,4- and 15% of the 2,6-dichloroacetanilides. No significant amount of the 2,5- or the 2,3-dichloro-isomers have been detected. The relative rate together with the product composition allow the calculation of the partial rate factors for the chlorination in the various positions. These when taken in conjunction with those recorded for acetanilide under similar conditions enabled indirect estimates to be made of the partial rate factor meta to chlorine. The results obtained are examined in the light of the ‘additivity principle.’