The fourth Uhuru catalog of X-ray sources.

Positions and intensities are presented for 339 X-ray sources observed by the Uhuru (SAS A) X-ray satellite observatory. We find good agreement between the sources in this catalog and those in the 3U and 2A catalogs. Optical and radio counterparts are suggested based on positional coincidence. The major classes of identified objects include binary stellar systems, supernova remnants, Seyfert galaxies, clusters of galaxies, and possibly the new class of superclusters of galaxies. Subject heading: X-rays: sources