The AA. have studied biological effects of laser radiation and methylene blue (MB) on Salmonella typhimurium TA 1538 strain. Their results show low lethal effect of laser radiation directly proportional to administered dose. This effect is more evident in the only MB treatment. Lethal effect persisted, although non directly proportional with combined treatment laser and MB. Some treatments have not demonstrated mutagenetic effect. A new set of trials they are making on Salmonella typhimurium TA 100 strain with plasmid pK M 101 that give to strain greatest susceptibility for mutagenetic agents.