  Quantum gravity may lead to an energy dependence in the speed of light. The
high energy radiation from gamma-ray pulsars can be used to place limits on
such effects. We find that emission from the Crab pulsar at energies above 2
GeV trails that at 70-100 MeV by no more than 0.35 ms (95% confidence) and
place a lower bound on the energy scale of quantum gravitational effects on the
speed of light of 1.8 x 10^15 GeV. This bound might be improved by two orders
of magnitude by observation of pulsations from the Crab at higher energies,
50-100 GeV, in the near future.
