The denaturation of hen egg-white lysozyme has been studied under a variety of denaturing conditions by difference spectroscopy, polarimetry, and viscometry. It has been found that the lysozyme molecule can take up four different denatured conformations, depending on the denaturant used. Urea and guanidinium chloride produce the most completely denatured state, IV, and, listed in the order of increasing residual structure, lithium chloride gives state III, temperature state II, and lithium perchlorate state I. Differences in the spectra at 300 nm have been a valuable aid in relating the different denatured states to each other.