The effect of an applied electric field on the electrical conductivity of potassium‐seeded acetylene‐air and hydrogen‐oxygen flame plasmas at atmospheric pressure has been explored experimentally. These flames, of interest for magnetohydrodynamic studies, were produced on a Meker‐type burner designed to give a seeded cylindrical core surrounded by an unseeded shield flame. The flow system, unconfined by walls, was particularly advantageous for conductivity measurements. The voltage gradient was determined by means of a floating double probe. The effective flame diameter, seed partial pressure and gas temperature were determined spectroscopically. Good agreement between measured and calculated conductivities was obtained for low current densities. The enhancement of the conductivity observed for increasing current density can be accounted for on the basis of Joule heating of the gas in the case of C2H2/air/K. No simple explanation for the enhancement in the case of H2/O2/K has been found.