  We apply several methods related to the WKB approximation to study
cosmological perturbations during inflation, obtaining the full power spectra
of scalar and tensor perturbations to first and to second order in the
slow-roll parameters. We compare our results with those derived by means of
other methods, in particular the Green's function method, and find agreement
for the slow-roll structure. Scalar wave propagation on the Schwarzschild
background is also considered.
