Let G=ResE/FH, where
H is a connected reductive group over a number field F
and E/F is a quadratic extension. We define the
regularized period of an automorphic form of G relative to
H, and we express the regularized period of cuspidal Eisenstein
series in terms of intertwining periods, which are relative analogues
of the standard intertwining operators. This leads to an analogue of
the Maass-Selberg relations. The regularized periods appear in the
contribution of the continuous spectrum to the relative trace
formula.