For use in virological tissue culture work, gentamicin is more convenient than penicillin + streptomycin. It is bactericidal for a wider range of organisms, may be used at only half the concentration needed for penicillin and streptomycin, does not apparently interfere with growth of tissue cultures and viruses, remains active at 37 degrees C., and, most remarkable of all, it is stable at autoclave temperatures and so can be put into media before sterilization, thus lessening the number of additions to the sterilized medium. Gentamicin is now in routine use in this laboratory.