Electrochemically prepared polypyrrole films have metallic conductivities in the range 40-100 S cm-1 whereas poly-N-methyl pyrrole films have conductivities more typical of a semiconductor, t/if 10-3 S cm-1. Films made by the electrochemical polymerization of mixtures of pyrrole and N-methyl pyrrole have redox potentials intermediate between those of either monomer, indicating that they are in fact random copolymers. The electrical conductivity and thermopower measured as a function of copolymer composition show no evidence for an abrupt metal-semiconductor transition. All these polymers are stable in air to temperatures in excess of 100°C. © 1981.