SUMMARYUsing the mica‐replication technique of Hall, it is possible to visualize small, metal‐shadowed biological macromolecules. Consideration is given to the interpretation of micrographs obtained in this way, in order that molecular dimensions may be inferred.It is shown that the width of the shadow cast by a macromolecule can be measured precisely. A method is developed whereby the histogram of the experimentally determined shadow widths is interpreted by reference to computer‐generated histograms, based upon models of assumed dimensions. Results are presented illustrating the use of this new m