It has become evident (Osborn, 1943; Lucas and Lewis, 1944) that higher plants are potential sources of antibiotic agents. Several investigators (Little and Grubaugh, 1946; Atkinson and Rainsford, 1946; Sanders, Weatherwax, and McClung, 1945) have reported antibiotic effects of juices and of crude extracts of plants on various microorganisms. The active materials can be separated in some degree of purity (Cavallito, Buck, and Suter, 1945; Cavallito, Bailey, and Kirchner, 1945; Heatley, 1944), and there is evidence that the agents so obtained can be introduced into the animal body and will control experimental infections (Carlson, Bissell, and Mueller, 1946). In screening several hundred plants (Carlson, Douglas, and Robertson, 1948) the authors observed that a species of sumac contained an antibiotic agent extractable in aqueous solutions. In later work this or similar agents were obtained from sumac by extraction with ethyl ether. It is the purpose of this paper to report the antibiotic activity of partially purified extracts from a species of sumac, Rhus hirta. METHODS Chemical procedures. Stems and leaves collected in the fresh state were finely chopped and sufficient ethyl ether was added to cover the material. Extraction was carried out for 24 to 48 hours at room temperature. The ether extraction (911B1) was separated from the plant residue by decanting. The plant residue was then allowed to stand at room temperature for 24 to 48 hours with an equal volume of distilled water (see flow chart, figure 1). The supernatant water extract (911B90) was decanted from the plant residue and was evaporated to dryness, yielding a brown, brittle material (9llB96). This material was partially soluble in distilled water as a red solution (911B97) with the persistence of some red-gray precipitate (911B98). Ten volumes of ethyl alcohol (95 per cent) were added to the red solution. A clear yellow supernatant and a gray precipitate (911B100) were obtained. The supernatant was evaporated to remove the alcohol. A dark brown solution remained (911B102). The ether was evaporated from the original extraction (911B3) leaving a green gum (911B15). The gum was placed in a Soxhlet extraction thimble and extracted with chloroform until colorless (approximately 5 hours). The chloroform was decanted and evaporated again leaving a thick green gum (911B50). The residue (911B47A), after chloroform extraction, was divided