Ovalbumin and S-ovalbwnin have been compared by measuring their viscosity and optical rotatory dispersion in aqueous formamide solutions at pH 7 and in urea solutions at pH 3�5; also by measuring the optical rotatory dispersion of heated solutions at different salt concentrations, and by a study of ultraviolet differlilnce spectra in alkylamine hydrochloride solutions. The different aggregation behaviour of the two proteins after denaturation suggests a difference in covalent bond structure.