  In this paper we study gauge-invariant metric fluctuations from a Noncompact
Kaluza-Klein (NKK) theory of gravity in a de Sitter expansion. We recover the
well known result $\delta\rho/\rho \simeq 2\Phi$, obtained from the standard 4D
semiclassical approach to inflation. The spectrum for these fluctuations should
be dependent of the fifth (spatial-like) coordinate.
