  Gravitational lensing in metric theories of gravity is discussed. I introduce
a generalized approximate metric element, inclusive of both post-post-Newtonian
(ppN) contributions and gravito-magnetic field. Following Fermat's principle
and standard hyphoteses, I derive the time delay function and deflection angle
caused by an isolated mass distribution. Several astrophysical systems are
considered. In most of the cases, the gravito-magnetic correction offers the
best perspectives for an observational detection. Actual measurements
distinguish only marginally different metric theories one from another.

Astrophysics