SUMMARY: Four strains of Salmonella typhimurium avirulent for mice were found to be capable of acting as gene acceptors in transduction experiments. An attempt was made to transduce virulence to three strains, using a typical mouse-virulent strain of S. typhimurium as donor. Two of the strains which are adenine-dependent were successfully made virulent by transduction and simultaneously became adenine-independent. The other strain M206, whilst possessing the typical antigenic structure of S. typhimurium and being non-exacting nutritionally, was not made virulent by transduction.