Fibrillar polypyrroles have been prepared by electrodeposition through honeycomb gamma-alumina membranes. The morphology has been extensively studied using field-emission scanning electron microscopy. The rate of fibre growth in several solvents has been measured by direct length measurement. The occupation of the host membrane pores by polypyrrole has been examined by ultramicrotome techniques. In extended polymerizations, both solid rods and tubes are found.