  We estimate the number of AGN among the galaxies in the Hubble Deep Field
(HDF). The recent discovery of a class of X-ray luminous narrow emission-line
galaxies has provided a possible explanation for the origin of the X-ray
background (XRB), although the nature of the activity is still unresolved. By
extrapolating the observed X-ray number count distribution to faint optical
magnitudes we predict that this AGN population could account for a significant
fraction, $\sim 10$ per cent, of the galaxies in the HDF. In contrast, normal
broad line QSOs are expected to account for no more than $\sim 0.1$ per cent of
the sources at these magnitudes.
