We show that polarized gamma p -> \pi^+ n in the threshold region is an
excellent candidate for measuring the leading parity-violating pion-nucleon
coupling h_{\pi NN}^{(1)} to an uncertainty of 20% if it has a natural size
from dimensional analysis. The conclusion is based on a large unpolarized cross
section, a new low-energy theorem for the photon polarization asymmetry at the
threshold A_\gamma|_{th} = \sqrt{2} f_\pi (\mu_p-\mu_n) h_{\pi NN}^{(1)}/g_A
m_N \sim h_{\pi NN}^{(1)}/2, and its strong dominance at forward and backward
angles in the threshold region.Comment: 4 pages, 3 figures. More data points in fig. 1 and note added in
proof adde
