BENZALKONIUM chloride (zephiran chloride®), introduced by Domagk1 in 1935, has become a popular disinfectant. A recent survey2 shows that in America it is currently used in approximately one seventh of the hospitals for disinfection of the hands and in one half of the hospitals for preparation of the field for operation. It is the best known and most widely used member of the rapidly growing group of quarternary ammonium compounds. In contrast to soap and other anionic substances, it is a cationic detergent. It is said to have keratolytic and emollient action.3 Its pH is near the neutral point. It is an efficient wetting agent, with relatively low surface tension. It is chemically stable. In ordinary concentrations it exhibits little if any toxicity4 and does not irritate the skin. If, in addition to these desirable qualities, benzalkonium chloride can be shown to be strongly and