  We study the microwave background anisotropy due to superhorizon-size
perturbations (the Grischuk-Zel'dovich effect) in open universes with negative
spatial curvature. Using COBE results on the low-order temperature multipole
moments, we find that if the homogeneity of the observable Universe arises from
an early epoch of inflation, the present density parameter cannot differ from
unity by more than the observed quadrupole anisotropy, $|1-\Omega_0| \alt Q
\simeq 5\times 10^{-6}$. Thus, inflation models with low $\Omega_0$ either do
not fit the microwave background observations or they do not solve the horizon
problem.
