The bacteriostatic effect of amnionic fluid was studied using three pathogenic organisms thich are encountered in the perinatal period, E. coli, S. aureus, and K. pneumoniae. Another organism, S. typhimurium, was included to find an antibacterial spectrum. Amnionic fluid inhibited the growth of all four organisms, with a wide degree of individual variation among specimens. The greatest degree of inhibition was noted for S. aureus and the least for K. pneumoniae at 6 hours incubated. At 24 hours incubated the former was noted for K. pneumoniae and the latter for S. typhimurium. The ability of amnionic fluid to inhibit the growth of certain pathogenic organisms may be significant in prevention of perinatal infection.