  We present results from a 20 h RXTE observation of Vela X-1, ncluding a
peculiar low state of a few hours duration, during which the pulsation of the
X-ray emission ceased, while significant non-pulsed emission remained. This
``quiescent state'' was preceded by a ``normal state'' without any unusual
signs and followed by a ``high state'' of several hours of increased activity
with strong, flaring pulsations. while there is clear spectral evolution from
the normal state to the low state, the spectra of the following high state are
surprisingly similar to those of the low state.
