  We report the detection of high frequency variability in the black hole X-ray
transient XTE J1650-500. A quasi-periodic oscillation (QPO) was found at 250 Hz
during a transition from the hard to the soft state. We also detected less
coherent variability around 50 Hz, that disappeared when the 250 Hz QPO showed
up. There are indications that when the energy spectrum hardened the QPO
frequency increased from ~110 Hz to ~270 Hz, although the observed frequencies
are also consistent with being 1:2:3 harmonics of each other. Interpreting the
250 Hz as the orbital frequency at the innermost stable orbit around a
Schwarzschild black hole leads to a mass estimate of 8.2 Msun. The spectral
results by Miller et al.(2002, ApJ, 570, L69), which suggest considerable black
hole spin, would imply a higher mass.
