Information theory formalism has been applied to the scanning electron microscope. A theoretical model of two‐dimensional secondary electron noise has been derived and the maximum capacity content per picture element of the S.E.M. has been computed as a function of its geometrical resolving power. According to the theory, it is shown that the maximum number of grey levels on the picture varies between 2 and 8 (varying with the maximum secondary electron yield) with a resolving power of 200 Å for a S.E.M. equipped with a tungsten filament gun, and 30–40 Å is equipped with a lanthanum‐hexaboride gun. However, these figures are established with the assumption that the object does not present any redundant properties. The knowledge of the statistics of a general class of objects will permit the use of adapted coding to increase the information content in the object area of interest.