EPR studies and HMO calculations are carried out in order to understand the nature of the electrolytically generated radical of 4(2′-thienyl)quinazoline (4-TQ) in dimethylformamide (DMF). Single broad EPR signal obtained is explained on the basis of theoretical hyperfine splitting constants. By correlating the experimental half-wave potentials and the colour of the radical with HMO energies, it is concluded that 4-TQ protonated at N1-position is getting reduced to give the neutral radical. © 1980, All rights reserved.