AbstractA treatment is given for the Brownian deformation of an elastic sphere which permits extension of the theory of the Maxwell effect of solutions of elastic spheres to arbitrary values of the ratio of the time of establishment θ′, of a preferential orientation to the deformation relaxation time θ of the sphere. For large values of η0/ηithe (ratio of solvent viscosity to internal viscosity) the effect reduces to the simple deformation effect described in previous papers. For decreasing values of η0/ηithe deformation effect is gradually replaced by the orientation effect (orientation of elongated configurations). The influence of the intensity of the fluctuations as measured by the mean square value δ02of the deformation coefficient is discussed. Values of δ0are given for a series of polystyrene samples of increasing molecular weight. The theory is in qualitative agreement with experimental results on solutions of chain molecules and leads in particular to a new interpretation of the data for thymonucleic acid. The incompatibility of the Kuhn and Kuhn dumbbell theory with experimental results is discussed in more detail than in previo