The various possible systems of a.c. magnetohydrodynamic power generation using electrodes or inductive coupling with stationary or alternating magnetic fields are examined and compared with the d.c. case.It is shown that with gas temperatures below 3000° K and an alternating magnetic field the cost of coil driving equipment is likely to be prohibitive, whilst theoretical and experimental evidence suggests that with inductive coupling and a steady magnetic field the power densities are probably too low to be of interest. The only possibility remaining is the generator with pulsed conductivity where the current is collected on electrodes and the considerable difficulties peculiar to this method are discussed.