Acidic or basic dyeing of fibers involves ionic interactions between reactive groups on the polymers and dye molecules. Such interactions can be utilized in the functional finishing of fabrics. This article discusses a new approach of employing the ionic interactions between anionic carboxylic end groups of polyamides and cationic quaternary ammonium salts in the chemical finishing of nylon fabrics to achieve desired durable antimicrobial functions. The finishing conditions such as pH, finishing temperature, and time were studied, and the pH of the finishing bath was very critical in affecting the ionic interactions and thus exhaustion of the salts on the fabrics. The finishing process should be carried out at a temperature above the glass transition temperature of nylon 66. The finished products demonstrated excellent durability of antimicrobial functions. (C) 2003 Wiley Periodicals, Inc.