  In this paper we demand that a successfull inflationary scenario should
follow from a model entirely motivated by particle physics considerations. We
show that such a connection is indeed possible within the framework of concrete
supersymmetric Grand Unified Theories where the doublet-triplet splitting
problem is naturally solved. The Fayet-Iliopoulos D-term of a gauge
$U(1)_{\xi}$ symmetry, which plays a crucial role in the solution of the
doublet-triplet splitting problem, simultaneously provides a built-in
inflationary slope protected from dangerous supergravity corrections.
