The methods of electron microscopy and optic difraction were used to determine the main parameters of the structural organization of cholera bacteriophage of serotype II. The virions of the phage under study were found to consist of a capsid of icosahedral shape and 77.4 X 66.1 nm in size, formed of 252 morphological subunits and having the cavity volume of 76.3 X 10(3) nm3. A process of 94.8 nm in length adheres to the capsid, with a shell capable of contractions, of 85.6 nm in length, 20.6 nm in width, containing 60 morphological subunits. The shell covers the central core of 8.9 nm in diameter. The optic difraction revealed the helical type of symmetry of the process structure and its main parameters.