  We put active galactic nuclei (AGNs) with low-mass black holes on the
fundamental plane of black hole accretion---the plane that relates X-ray
emission, radio emission, and mass of an accreting black hole---to test whether
or not the relation is universal for both stellar-mass and supermassive black
holes. We use new Chandra X-ray and Very Large Array radio observations of a
sample of black holes with masses less than $10^{6.3}\ M_{\scriptscriptstyle
\odot}$, which have the best leverage for determining whether supermassive
black holes and stellar-mass black holes belong on the same plane. Our results
suggest that the two different classes of black holes both belong on the same
relation. These results allow us to conclude that the fundamental plane is
suitable for use in estimating supermassive black hole masses smaller than
$\sim 10^7\ M_{\scriptscriptstyle \odot}$, in testing for intermediate-mass
black holes, and in estimating masses at high accretion rates.
