Heat generation by direct electric conduction in a fully developed channel flow was studied to clarify interaction between the hydrodynamic, electric and thermal phenomena involved. The equations governing the system were solved numerically by a finite volume code. It was found that the difference between the residence time of the fluid flowing close to the wall and in the center of the channel causes deformation of the velocity profiles. This phenomenon creates a competition between the fluid particles flowing in these two regions and results in equalizing the temperature and velocity distribution in the channel span. An experimental investigation carried out in parallel with the numerical study yielded good agreement. An array of longitudinal streaks found on the channel electrode wall, with LIF visualization, is attributed to an instability phenomenon caused by electric body force. The wavelength of the streaks was measured and the control parameters of the instability were determined.