  We study the shift of the chiral condensate in a constant electromagnetic
field in the context of chiral perturbation theory. Using the Schwinger
proper-time formalism, we derive a one-loop expression correct to all orders in
$m_{\pi}^2 / eH$. Our result correctly reproduces a previously derived
``low-energy theorem'' for $m_\pi = 0$. We show that it is essential to include
corrections due to non-vanishing $m_\pi$ in order for a low energy theorem to
have any approximate regime of validity in the physical universe. We generalize
these results to systems containing electric fields, and discuss the regime of
validity for the results. In particular, we discuss the circumstances in which
the method formally breaks down due to pair creation in an electric field.
