  We show by a numerical procedure that a short-range interaction $u$ induces
extended two-particle states in a two-dimensional random potential. Our
procedure treats the interaction as a perturbation and solve Dyson's equation
exactly in the subspace of doubly occupied sites. We consider long bars of
several widths and extract the macroscopic localization and correlation lengths
by an scaling analysis of the renormalized decay length of the bars. For $u=1$,
the critical disorder found is $W_{\rm c}=9.3\pm 0.2$, and the critical
exponent $\nu=2.4\pm 0.5$. For two non-interacting particles we do not find any
transition and the localization length is roughly half the one-particle value,
as expected.
