We consider the effect of dark matter in the form of multi-Ev axions o
n the extragalactic background light. Our treatment differs from that
of other workers in that we assume axions to be clustered in Galactic
halos, with nonzero velocity dispersions. We also approach the problem
in a fully general relativistic manner, treating the axion halos as l
uminous elements of a pressure-free perfect fluid in a standard Friedm
ann-Robertson-Walker universe. We find that the ultraviolet extragalac
tic background light places a firm upper limit of 9 eV on the axion re
st energy, and that this drops to 4 eV for the simplest axion models,
all but closing the multi-eV axion window (which begins at 3 eV). Thes
e results are close to earlier upper limits of 5 and 8 eV derived from
the extragalactic background by Turner and Ressell, respectively. Alt
hough our methods differ somewhat from theirs, our findings support th
eir conclusion that axions, if they exist, are likely to have rest ene
rgies well below the eV range.