Under the Tropical Deterioration Administrative Committee of the National Defense Research Committee there was established in July 1944 a Subcommittee on Synthetic Resins, Plastics and Plasticizers to consider the problems of tropical deterioration of these materials. The following topics are discussed: Methods for the determination of the resistance of plastic materials to fungal attack; The susceptibility of pure resins to fungal attack; Susceptibility of plasticizers and other components to fungal attack; The effect of fungal growth on properties of plastics; Comparison of plastics containing fungicides with control samples; and an outline of a method for determining the relative fungus resistance of plastic materials.