To identify the primary mechanisms of the biological activity of electrostatic field (ESF),we conducted the investigations of the influence of field on the structure of natural biological membranes.In accordance with our earlier studies the extemal in vivo influence of ESF leads to the redistribution and change of the surface charge of rat erythrocytes.At this stage,we have carried out a series of spectrofluorometric studies of the physical parameters (viscosity,microviscosity,polarity,the immersion degree of membrane proteins in lipid bilayer)of rat erythrocyte ghosts after 1-hour in vivo exposure of animals to the 200kV/m field.