Ferromagnetic behavior at room temperature is reported in metal-free-conducting polymer samples of poly(3-methylthiophene) doped with ClO4-. Magnetic moments associated with spin 1/2 positive polarons are possibly interacting through a Dzialoshinski-Moriya anisotropic superexchange via the dopant anions, giving rise to weak ferromagnetism. (C) 2001 Elsevier Science BY. All rights reserved.