  We prove that there exists a diffusion process whose invariant measure is the
three dimensional polymer measure $\nu_\lambda$ for small $\lambda>0$. We
follow in part a previous incomplete unpublished work of the first named author
with M. R\"ockner and X.Y. Zhou. For the construction of $\nu_\lambda$ we rely
on previous work by J. Westwater, E. Bolthausen and X.Y. Zhou. Using
$\nu_\lambda$, the diffusion is constructed by means of the theory of Dirichlet
forms on infinite-dimensional state spaces. The closability of the appropriate
pre-Dirichlet form which is of gradient type is proven, by using a general
closability result in [AR89a]. This result does not require an integration by
parts formula (which does not even hold for the two-dimensional polymer measure
$\nu_\lambda$) but requires the quasi-invariance of $\nu_\lambda$ along a basis
of vectors in the classical Cameron-Martin space such that the Radon-Nikodym
derivatives have versions which form a continuous process.
