  We investigate the clustering properties of galaxies in the recently
completed ELAIS-S1 redshift survey through their spatial two point
autocorrelation function. We used a sub-sample of the ELAIS-S1 catalog covering
approximately 4 deg^2 and consisting of 148 objects selected at 15 micron with
a flux >0.5 mJy and redshift z<0.5. We detected a positive signal in the
correlation function that, in the range of separations 1-10 h mpc is well
approximated by a power law with a slope gamma = 1.4 and a correlation length s
=5.4 h mpc. This result is in good agreement with the redshift-space
correlation function measured in more local samples of mid infrared selected
galaxies like the IRAS PSC$z$ redshift survey. This suggests a lack of
significant clustering evolution of infrared selected objects out to $z=0.5$
that is further confirmed by the consistency found between the correlation
functions measured in a local (z<0.2) and a distant (0.2<z<0.5) subsample of
ELAIS-S1 galaxies. We also confirm that optically selected galaxies in the
local redshift surveys, especially those of the SDSS sample, are significantly
more clustered than infrared objects.
