  We derive novel low--energy theorems for single pion production off nucleons
through the isovector axial current. We find that the $k^2$-dependence of the
multipole $L_{0+}^{(+)}$ at threshold is given by the nucleon scalar form
factor, namely $\sigma(k^2-M_\pi^2 ) /(3 \pi M_\pi F_\pi )$. The relation to
PCAC results for soft pions including electroweak form factors is also
clarified.
