IT has been previously noted that growth of a number of bacterial species is inhibited in vitro by herpes simplex virus propagated in a variety of antibiotic-free cell lines1. 0.1 ml. of such tissue culture fluid, applied to 1 cm2 of sterile thick filter paper, placed on a Petri plate surface-seeded with 0.2 ml. of a standardized inoculum of a 6-h bacterial culture on a medium containing equal parts of mixed 1 per cent trypticase in 2 per cent agar and monkey kidney B medium Melnick, was found to produce a distinct inhibitory zone around the virus-impregnated filter square with bacterial strains belonging to a number of different species after 16-18 h incubation at 37° C, providing sufficient concentration of virus is present. Allantoic fluid derived from 9-day-old chick embryos the chorioallantoic membranes of which had been infected with 2 herpes simplex virus strains failed to suppress the bacterial growth. Control tissue culture fluid, not inoculated with virus, was similarly ineffective in this regard.