It is shown that lysozyme solutions exhibit thixotropic properties down to the very low concentration of 10−4 by weight. The entire range of concentration up to 30% by weight is investigated. It is found that there are three ranges, namely, from 10−4 to 2×10−3; from 3×10−3 to 10−2, and larger than 15%, each of them characterized by different behavior. Thixotropic properties can be explained in terms of the building up of a structure that is both time and shear dependent. It is also shown that a yield point exists. From the experimental results the time constant of the process, the yield point, and the dependence on the shear rate are found.