A tincture and an aqueous solution containing 0.5% of 1,6-di-4′-chlorophenyl-diguanidohexane were tested in vivo as preoperative skin antiseptics. Skin biopsies were taken from various operative sites before and after a measured time of exposure to the antiseptic. Various periods of exposure were employed. The antiseptic was neutralized immediately at the end of the exposure time and bactericidal activity was tested by a standardized series of culture procedures. Tested under these conditions both the 0.5% aqueous solution and the 0.5% tincture possess marked skin disinfecting properties against a wide range of microorganisms.