Abstract: The present invention is concerned with novel antimicrobial thienyliodonium salts and methods and compositions employing the same, and is particularly directed to a class of thienyliodonium salts which are of value as antimicrobials and microbicides for the control of many bacterial organisms such as the gram-negative and gram-positive types, the molds, the mildews, the fungi and the slimes, and are of particular value for the preservation of paper, plaster, wallboards, fabric, textiles, cooling waters, plasticizers, latices, polymers, resins, adhesives, inks, paints, fuels, cutting oils, greases, seeds, terrestrial plants, detergents, soaps, shampoos and wood.