  If massive black holes constitute the dark matter in the halo surrounding the
Milky Way, the existence of low mass globular clusters in the halo suggests an
upper limit to their mass, $M_{_{BH}}$. We use a combination of the impulse
approximation and numerical simulations to constrain $M_{_{BH}} \lsim
10^3M_\odot$, otherwise several of the halo globular clusters would be heated
to disruption within one half of their lifetime. Taken at face value, this
constraint is three orders of magnitude stronger than the previous limit
provided by disk heating arguments. However, since the initial mass function of
clusters is unknown, we argue that the real constraint is at most, an order of
magnitude weaker. Our results rule out cosmological scenarios, such as versions
of the Primordial Baryonic Isocurvature fluctuation model, which invoke the low
Jeans mass at early epochs to create a large population of black holes of mass
$\sim 10^6M_\odot$.
