Fungicides used to protect textile materials have previously been evaluated on the basis of the rate of tensile strength loss by treated fabrics after exposure to microbiological attack. This approach has been based on the assumption that loss of tensile strength is a gradual process beginning soon after exposure. In the present paper, It is demonstrated that fabrics treated with copper 8-quinolinolate are not susceptible to microbiological attack in soil burial until most of the fungicide has been lost. It is therefore advocated that future attempts to prevent microbiological deterioration by fungicide treatment emphasize the study of factors influencing the permanence of the fungicide on treated material. The method of studying the kinetics of fungicide loss is illustrated with data for residual copper 8-quinolinolate. The loss of this fungicide theoretically appears to be a zero-order reaction, although the experimental persistence curve is slightly curvilinear.