The Hamburg/RASS optical identification project
  We use digitized Schmidt direct and prism plates taken for the northern hemisphere Hamburg Quasar Survey (HQS) to obtain optical identifications for all high galactic latitude X-ray sources in the ROSAT Bright Source Catalogue (RASS-BSC) at |b|>=30 deg and DEC >= 0deg. In this part of the sky the RASS-BSC contains about 5300 X-ray sources. Presently, identifications exist for about 4100 RASS-BSC sources in this galactic latitude range. 
F.-J. Zickgraf, D. Engels, H.-J. Hagen, D. Reimers