  The cross section for the diffractive reaction gamma* + p -> c cbar + p with
a real or virtual photon is calculated in the nonperturbative two-gluon
exchange model of Landshoff and Nachtmann. Numerical predictions are given for
cross sections and spectra at typical HERA values of c.m. energy and photon
virtuality. The contribution of charm to the diffractive structure function is
evaluated and found to be rather small in the model, and the ratio between the
production rates for b bbar and c cbar is tiny.
