[en] The polarographic behaviour of tetravalent U, Np and Pu hexachloride complexes of composition (Et₄N)₂AnCl₆ in acetonitryl on mercury drop electrode has been studied. The reduction was found to involve two stages, first to the three-valent state, than to an amalgam. All the waves shown by the complexes are irreversible. On a rotating platinum microelectrode the complexes are polarographically inactive. It is shown that An(4) in acetonitryl forms strong complexes with chloride ions. Thus the potentials of the half-waves corresponding to the reduction into An(3) are very negative