  The X-ray spectrum obtained by Tanaka et al from a long observation of the
active galaxy MCG$-6-30-15$ shows a broad iron K$\alpha$ line skewed to low
energies. The simplest interpretation of the shape of the line is that it is
due to doppler and gravitational redshifts from the inner parts of a disk about
a massive black hole. Similarly broad lines are evident in shorter observations
of several other active galaxies. In this paper we investigate other line
broadening and skewing mechanisms such as Comptonization in cold gas and
doppler shifts from outflows. We have also fitted complex spectral models to
the data of MCG$-6-30-15$ to see whether the broad skewed line can be mimicked
well by other absorption or emission features. No satisfactory mechanism or
spectral model is found, thus strengthening the relativistic disk line model.
