As an application of the recently proposed Langevin formulation of qua
ntum dynamics, we quantize the time-dependent harmonic oscillator. In
this way, we are able to explicitly compute the quantum-mechanical pro
pagator. At variance with previous results, the expression found in th
is letter contains no auxiliary function to be determined by solving (
as yet unsolved) non-linear differential equations, but it is written
in terms of two series which arise quite naturally within the present
formalism. Our strategy is compared with ordinary time-dependent pertu
rbation theory.