  We study the bispectrum of the curvature perturbation on uniform energy
density hypersurfaces in models of inflation with two scalar fields evolving
simultaneously. In the case of a separable potential, it is possible to compute
the curvature perturbation up to second order in the perturbations, generated
on large scales due to the presence of non-adiabatic perturbations, by
employing the $\delta N$-formalism, in the slow-roll approximation. In this
case, we provide an analytic formula for the nonlinear parameter $f_{NL}$. We
apply this formula to double inflation with two massive fields, showing that it
does not generate significant non-Gaussianity; the nonlinear parameter at the
end of inflation is slow-roll suppressed. Finally, we develop a numerical
method for generic two-field models of inflation, which allows us to go beyond
the slow-roll approximation and confirms our analytic results for double
inflation.
