  We calculate the cross-section for the thermal $n+p\rightarrow d+\gamma$
process in chiral perturbation theory to next-to-next-to-leading order using
heavy-fermion formalism. The exchange current correction is found to be
$(4.5\pm 0.3)~\%$ in amplitude and the chiral perturbation at one-loop order
gives the cross section $\sigma_{th}^{np}=(334\pm 2)\ {\mbox mb}$ which is in
agreement with the experimental value $(334.2\pm 0.5)\ {\mbox mb}$. Together
with the axial charge transitions, this provides a strong support for the power
of chiral Lagrangians for nuclear physics.
