The structure and the magnetic properties of polaronic high-spin (HS) pi-conjugated one-dimensional (1-D) polymers (systems) with stable polymethine radicals of Wurster's and Weitz types within the elementary units have been investigated theoretically. Using the band theory the nature and magnitude of the magnetic coupling between the electrons within the half-filled band (HFB) of the polymers were determined. It was shown that the electrons are ferromagnetically (FM) coupled with an effective exchange integral J(eff) similar to 0.1 eV for polymers with Wurster's type radicals, and J(eff) similar to 0.01 eV of polymers with Weitz type radicals, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.