We investigate here defects in initially ordered polymers of 5,6-indolequinone, in one or other redox form. The defects studied include aggregation of the carboxyl radical into one skeleton monomer, the aggregation of a host monomer in a lateral misplaced position, and faults in the polymerization sequencing. Our study is carried out, as in the first paper I, through Hückel π-electron theory, and results are compared to the perfect structures in I. Our results indicate that the end-type defect suggested as an electron capture center in I is not deactivated by these other structural defects, and that new capture centers might be introduced that could also be responsible for the acceptor behavior of melanins. © 1990 American Institute of Physics.93428482853