  The possibility of thermally induced initial density perturbations in
inflationary cosmology is examined. The fluctuation dynamics of a scalar field
plus thermal bath system during slow roll is described by a Langevin-like
equation. Fluctuation-dissipation arguments show that for a wide parameter
range within the standard inflation model, the thermal fluctuations of the
scalar field can dominate its quantum fluctuations. The initial amplitude of
density perturbations is found to lie in a range which is consistent with the
recent observations of cosmic temperature fluctuations.
