Different dilutions of chlorhexidine gluconate were tested by the Kelsey-Sykes procedure. The method was further modified on microtitration plates using 2,3,5-triphenyltetrazolium chloride (TTC) reduction as an indicator of bacterial growth. There was a good correlation with the results based on TTC reduction and the conventional method based on turbidity changes caused by bacterial growth. Furthermore, the modified method using TTC reduction is more rapid and can be read by the naked eye because of the red colour.