Einstein Observatory Imaging Proportional Counter X-ray observations of fields in SA 57, SA 68, and U Mi that possess deep optical and radio coverage have been conducted with a sensitivity comparable to that of the Einstein Observatory's medium sensitivity survey of serendipitous X-ray sources. The number of X-ray sources detected is consistent with a log N(greater than S) - log S slope of about -1.5. The fraction of active galactic nuclei in the X-ray sample is less than about 50 percent, with the rest being composed of clusters and normal galaxies, consistent with the medium sensitivity survey.