Vapors of 133 essential oils were screened in uipro f?r antibaaerirl activity against six test organisms. One hundred and five vapors were found to possess antibacterial activity on at least one of the test or anisrns. Vapors of thyme (white), cassia, i y m e (red), savory, cinnamon, origanum, and cherry laurel produced prominent zones of inhibition with all test organisms. Gram-positive bacteria were more susceptible to the vapors than Gramnegative bacteria. TUDIES on the action of essential oil vapors on anthrax spores were reported in 188i by Chamberlain (1). Subsequent investigatiqns b y Greig-Smith (2), Macht and Kunkel (3), Morel and Rochaix (4, 5), Schobl and Kusama ( G ) , Coulthard ( i ) , Remlinger and Railly (S), and recently by Ryu (9) and Grubb (10) have clearly demonstrated that essential oil vapors possess antibacterial properties. Yet the proper evalua-Antibacterial Activitv of Essential Oil VaDors * 692 ~~ *Received February 2. 1960. from the Department of Biology Long Island University Brooklyn N. Y. Thisiaperis based upon a theiissubmittid to the Graduate School of Long Island University by Nicholas A. Sicurella in partial fulfillment of the requirements for the degree of Master of Science.