In the course of attempts to purify the antibacterial agent we had extracted from Spanish moss (Tillandsia usneosides) (1), by adsorption on charcoal, we found that a powerful antibacterial substance for certain organisms could be recovered from charcoal itself. Blood charcoal and previously acidified animal charcoal contained it, but norit did not. This antibacterial substance recovered from charcoal proved to be elemental sulfur?Although sulfur is one of the oldest remedies known to man surprisingly little experimental work has been carried out with it. Colloidal sulfur was first prepared in 1888 (2), and since then many preparations have been used in the treatment of different conditions with varying degrees of success. It has been administe.red orally and by injection in the treatment of mental disease 0-5), by injection in the treatment of arthritis (6-8), and topically, as a fungicide in the treatment of cutaneous infections (9, 10). In both the precipitated and the colloidal forms, sulfur has been used extensively with notable success in the treatment of certain plant diseases (11,12).It is generally assumed that the size of the sulfur particles is basic in the activity of a preparation, the smaller the particles the more active the preparation obtained. In the skin it is thought that the particles of sulfur are converted through the medium of certain cells in the epidermis to sulfur-containing compounds (for example sulfides or pentathionic acid) and that these compounds are responsible for the antimicrobial action (9, 10).We are aware of only two reports of experiments showing the in vitro antimicrobial activity of sulfur upon human pathogenic organisms. The first was of experiments conducted in 1934 by Lawson (13), who investigated the effect of precipitated sulfur incorporated into Corper's mashed-potato medium on the growth of tubercle bacilli. He found that the addition of as little as 3 rag. of sulfur to 100 cc. of medium completely inhibited the growth of this organism. He stated that sulfur appears to have no inhibitory effect upon the growth of some of the ordinary pathogenic bacteria, not specified by him.The second report was of experiments conducted in 1935 by Kingery (14) who'stated that colloidal sulfur was fungicidal and fungistatic for Trichoi~hyton interdigitale and tinea corporis. The fungicidal experiments were carried out by adding a broth suspension of the organism to be tested, to a 1 per cent or 5 per cent dilution of colloidal sulfur. The mixture was shaken for 2 minutes and then several loopfuls were streaked on a suitable agar medium. No growth occurred in the streaks from the preparation a We are indebted to Dr. E. G. Miller, Jr., for these analyses. 531