We have derived the X-ray luminosities of a sample of galaxies in groups , making careful allowance for contaminating intragroup emission .
The L _ { X } : L _ { B } and L _ { X } : L _ { FIR } relations of spiral galaxies in groups appear to be indistinguishable from those in other environments , however the elliptical galaxies fall into two distinct classes .
The first class is central-dominant group galaxies which are very X-ray luminous , and may be the focus of group cooling flows .
All other early-type galaxies in groups belong to the second class , which populates an almost constant band of L _ { X } /L _ { B } over the range 9.8 < \log L _ { B } < 11.3 .
The X-ray emission from these galaxies can be explained by a superposition of discrete galactic X-ray sources together with a contribution from hot gas lost by stars , which varies a great deal from galaxy to galaxy .
In the region where the optical luminosity of the non-central group galaxies overlaps with the dominant galaxies , the dominant galaxies are over an order of magnitude more luminous in X-rays .

We also compared these group galaxies with a sample of isolated early-type galaxies , and used previously published work to derive L _ { X } : L _ { B } relations as a function of environment .
The non-dominant group galaxies have mean L _ { X } /L _ { B } ratios very similar to that of isolated galaxies , and we see no significant correlation between L _ { X } /L _ { B } and environment .
We suggest that previous findings of a steep L _ { X } : L _ { B } relation for early-type galaxies result largely from the inclusion of group-dominant galaxies in samples .