  We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50-1000 Hz and having a negative
frequency time derivative with magnitude between zero and $10^{-8}$ Hz/s. Data
from the fourth LIGO science run have been used in this search. Three different
semi-coherent methods of summing strain power were applied. Observing no
evidence for periodic gravitational radiation, we report upper limits on strain
amplitude and interpret these limits to constrain radiation from rotating
neutron stars.
