Some peculiarities of hydrophobic structure of serum albumine of some mammals were studied by NMR-spectroscopy, solubilization and fluorescent probes. It has been shown that the FNA probe is bound to the most hydrophobic cavities in the protein molecules, and the sizes of these regions in mammalian albumines are very close. The data obtained by ANS probe show that there exists a proportional relationship between the fluorescence intensity, the total volume of hydrophobic cavities and the quantity of "bound water". When using the ANS--Mg1/2 probe in all cases an increase of fluorescence intensity was obtained. It was concerned with the stabilizing effect of magnesium ions on the protein molecule.