This study attempted at microwave mutagenesis of: (i) Lactobacillus plantarum for lactic acid overproduction, and (ii) Streptococcus mutans for reduced lactic acid production. Lactic acid is among the microbiological products with high market potential. Lactic acid is also an important virulence factor in formation of dental caries by S. mutans, as the acid produced by the bacteria leads to demineralisation of the teeth. Two of the mutants obtained (one from each organism) were able to maintain the altered lactic acid production till 10 generations. However the magnitude of alteration in lactic acid producing ability of the mutants went on decreasing over generations. The microwave effects observed in this study seem largely to be athermal in nature. Investigation of the mutants obtained at molecular level may result in identification of novel mutations responsible for altered lactic acid production. These mutations can then be introduced into a suitable organism either for better industrial production of lactic acid, or for constructing new probiotic strain(s) for possible application in maintenance of oral health.