The periodic surface microstructure of an iron cylinder is revealed under its corrosion in a solution of nitric acid in a constant magnetic field. The temporary dependencies of the microstructure parameters have been obtained for the cylinders with different diameters and lengths. The effect of microstructuring is a new example of nonlinear self-organization in a magnetic field. The results of the paper can be used for controlled etching of metallic surfaces with the help of a magnetic field application. (c) 2005 Published by Elsevier B.V.