We present a cross-correlation between the ELAIS 15 \mu m ISO survey with the ROSAT ( 0.1-2 keV ) all-sky survey and the pointed observations WGACAT source catalogue .
The resulting sample contains 15 objects .
Optical spectroscopic identifications exist for 13 objects : 6 broad-line QSOs , 4 narrow line galaxies or type-2 AGN ( NLG ) and 3 stars .
We have used both the X-ray to IR luminosity flux ratio f _ { x } / f _ { IR } and the X-ray hardness ratios diagnostics to estimate the amount of obscuration in these objects .
The X-ray spectrum of the narrow-line galaxies does not present strong evidence for obscuration ; however , the low f _ { x } / f _ { IR } ratio combined with the high X-ray luminosities suggest that at least one of the narrow line galaxies is associated with an obscured Seyfert nucleus .
4 out of 6 QSOs present high f _ { x } / f _ { IR } ratios and steep X-ray spectra with \Gamma > 2 .
One QSO ( ELAISC15-J133442+375736 ) at a redshift of z=1.89 , has an abnormally low X-ray/IR flux ratio , with its infrared luminosity approaching that of an hyperluminous galaxy ( \sim 10 ^ { 12.98 } h ^ { -2 } L _ { \odot } ) .
Finally , one radio-loud QSO is the hardest X-ray source in our sample , presenting strong evidence for a high absorbing column ( N _ { H } \sim 10 ^ { 22 } cm ^ { -2 } ) .

Keywords : Cosmology : observations - X-ray : galaxies- Infrared : galaxies