In this non-technical article, the author discusses yellowing of textiles during storage in the absence of light and excessive heat, especially if oxides of nitrogen are present. Techniques for measuring nitrogen dioxide concentration qualitatively (Saltzman reagent) and quantitatively are discussed. Instruments required are listed, techniques described briefly, and the capability of each technique is described. Results of tests at a storage/distribution center, a manufacturing plant, and garment warehouse in Britain are presented. -- AATA