  For a finite reflection group on $\b R^N,$ the associated Dunkl operators are
parametrized first-order differential-difference operators which generalize the
usual partial derivatives. They generate a commutative algebra which is - under
weak assumptions - intertwined with the algebra of partial differential
operators by a unique linear and homogeneous isomorphism on polynomials. In
this paper it is shown that for non-negative parameter values, this
intertwining operator is positivity-preserving on polynomials and allows a
positive integral representation on certain algebras of analytic functions.
This result in particular implies that the generalized exponential kernel of
the Dunkl transform is positive-definite.
