The post-Newtonian, relativistic (1/c/sup 2/) tidal force is calculated within the general PPN framework of all metric theories of gravity. There are no relativistic tides in general relativity, but they are generally nonzero in other metric theories of gravity, including scalar-tensor theories. In close binaries (GM/c/sup 2/Rroughly-equal10/sup -6/), such as the binary pulsar system PSR 1913+16, the relativistic tides can be orders of magnitude larger than Newtonian tides. In ''preferred frame'' theories of gravity in which the PPN coefficient ..cap alpha../sub 1/ is nonzero, the relativistic tidal field is not the gradient of a scalar potential, but includes also a circulating, nonconservative field in a body.