  We present an analysis of the high frequency timing properties of the
April-May 2000 outburst of the black hole candidate and Galactic microquasar
XTE J1550-564, measured with the Rossi X-ray Timing Explorer. The rapid X-ray
variability we measure is consistent with the source being in either the ``very
high'' or ``intermediate'' black hole state. Strong (5-8% rms) quasi-periodic
oscillations (QPOs) are found between 249-276 Hz; this represents the first
detection of the same high frequency QPO in subsequent outbursts of a transient
black hole candidate. We also present evidence for lower-frequency QPOs at
approximately 188 Hz (3.5 sigma, single trial), also reported previously and
likely present simultaneously with the higher-frequency QPOs. We discuss these
findings within the context of the 1998 outburst of XTE J1550-564, and comment
on implications for models of QPOs, accretion flows, and black hole spin.
