Three primary mechanisms of paper deterioration in library and archival collections are driven by climatic conditions of excessive relative humidity. These are chemical reactivity, mechanical stress and biological deterioration. It is the view of the researcher that the role of chemical reactivity has not been adequately assessed in relation to the deterioration of paper. The significance of an autoxidative phenomenon, similar to the brown tideline staining at the wet/dry interface, has not been previously recognised as a cause of deterioration as an accelerated function of time under humid conditions of the macroclimate, and as a function of the unstable equilibrium moisture content of materials in a microclimate, but has been obscured by the accepted explanation of biological deterioration. An analytical procedure was developed to enable the comparison of oxidative degradation products found in stained areas of naturally aged samples with those formed during a dynamic simulated ageing programme to induce cellulosic discolouration. A relationship between the degradative mechanism and humid climatic conditions was established. Based on the findings of the analytical investigation, this study forms a contribution towards the development of a theory of deterioration. Evidence is presented of a chemical process of degradation in the oxidation of paper at the wet/dry interface, following the condensation and evaporation kinetics induced by cycling relative humidity (RH) driven by temperature fluctuations in diurnal and seasonal ranges. Sites of moisture accumulation at which the oxidative reaction readily take place, and which constitute a wet/dry interface, are identified at surface areas exposed to atmospheric exchange, in physical defects, in uneven adhesive lamination, in local wet treatments, in impervious storage enclosures or adjacent to an impervious surface which acts as a vapour barrier to the transudational force of capillary action. In advancing the theory of a chemical response of library and archival materials in the fluctuating moisture content as an explanation for the causation of cellulosic staining, the evidence of foxing is redefined. Librarians, archivists and conservators are thus assisted in the identification of the basic chemical reactions involved in the process of deterioration, and in recognising the role of oxidative degradation relation to environmental conditions. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.