  We report the discovery of a quasi-periodic oscillation (QPO) in data
obtained with the Rossi X-ray Timing Explorer of the dipping and eclipsing
low-mass X-ray binary EXO 0748-676. The QPO had a frequency between 0.58 and
2.44 Hz changing on time scales of a few days, an rms amplitude between 8% and
12%, and was detected in the persistent emission, during dips and during type I
X-ray bursts. During one observation, when the count rate was a factor 2 to 3
higher than otherwise, the QPO was not detected. The strength of the QPO did
not significantly depend on photon energy, and is consistent with being the
same in the persistent emission, both during and outside the dips, and during
type I X-ray bursts. Frequency shifts were observed during three of the four
X-ray bursts. We argue that the QPO is produced by the same mechanism as the
QPO recently found by Jonker et al. (1999) in 4U 1323-62. Although the exact
mechanism is not clear, it is most likely related to the high inclination of
both systems. An orbiting structure in the accretion disc that modulates the
radiation from the central source seems the most promising mechanism.
