It is found that for nearly all the proteins under study, the value of 1/P0', cut off on the ordinate by the extrapolation of the dependencies 1/P = f(T/eta . /tau B), is larger than the value of 1/P0 for model compounds--tryptophan, N-acetyltryptophan, glycyl-tryptophan. It is shown, that this may indicate the existence both of high-frequence intramolecular mobility, with the relaxation time rho much less than tau, and low-frequency intramolecular mobility the magnitude rho of which is of the same order as tau, independent on the medium viscosity. This peculiarity in the interpretation of the data, received by the method of rotational depolarization of UV-fluorescence of proteins arises because some tryptophan residues within the macromolecules of proteins are not accessible to the molecules of the solvent and that is why the rotational relaxation time of their intramolecular mobility is not dependent on the viscosity of the solvent. It is indicated that intramolecular mobility is inherent in tryptophan residues both with short wave and long wave spectrum of UV-fluorescence. The relaxation time, measured by the method of fluorescence depolarization, appeared to be smaller than that calculated for the short axe of an equivalent ellipsoid of revolution for a series of proteins (lysozyme, trypsin, pepsin, bovin serum albumin in acid medium, myelin basic protein). This indicates the existence of intramolecular mobility the magnitude rho of which is of the same order as tau dependent on the solvent viscosity in these proteins. Zymogens--trypsinogen and pepsinogen do not have such intramolecular mobilities.