The aim of this study was to characterise the kinetics of chlorine consumption and of inactivation of indicator bacteria in secondary wastewater using a batch laboratory reactor. In this time-course study, different concentrations of chlorine, used as NaOCl, were injected into the reactor, the levels of the different forms of residual chlorine were measured, and the numbers of faecal coliforms and faecal streptococci were determined. The results of the kinetics of chlorine consumption showed that monochloramines and trichloramines were the more important forms of residual chlorine as compared to free chlorine and dichloramines. The high contents of trichloramines indicated that the reaction of chlorine with ammoniacal nitrogen was very fast and that the transformation of chlorine into trichloramines was carried out in a time shorter than I min. Experimental results showed that the application of the model of Chick-Watson in its original form was not representative of the kinetics of inactivation of faecal coliforms and faecal streptococci. Modification of this model, in considering an initial reduction just at the contact of water with chlorine, improved the results of adjustment of the model. The same findings are valid for the model of Collins-Selleck in considering a value m imposed to the concentration of residual chlorine, since it appeared clearly that the concentration of chlorine influenced the output of disinfection more than did the time of contact.