a batch reactor was employed having ph meter, ir probe and continuous operation detectors so that it could work as a cstr reactor. as esterification advanced, then ir bands corresponding to the carboxyl acid cooh group and the alcohol c-oh group decreased whilst a parallel increase was presented in the ester -coor group band which was forming. reaction progress could be observed by continuous ir spectrum registration. the ir band for hoh (water) could not be studied because it needed a completely anhydrous medium for doing so. standard solutions could be prepared for quantifying ir band peak intensity, according to a component？s composition in the mixture. however, when phase changes occurred in the reaction mixture, this method could not be employed for following the course of a particular reaction because random variation was detected in band intensity.