Stopping powers of MeV hydrogen, helium and lithium ions at identical velocities in five different materials have been measured. They do not strictly obey the Z 1 2 dependence of the Bethe formula. Ratios between hydrogen and helium stopping powers scale as theoretical results of Ashley et al. and Jackson and McCarthy, while our lithium data are at variance with these theories. All data are, however, consistent with Lindhard's recent Z 1 3 correction combined with Bloch's Z 1 4 correction.