The inherent advantage of anti-coincidence counting of low-level radioactivity is defined in terms of changes in the limits of decision, detection and determination. It appears that the advantage factor can be expressed in the experimentally observed reductions of peak area, compton continuum and natural background. For an array equipped with a sample changer the advantage factor for interference by the compton continuum is4, while that for interference by the natural background amounts to
3. By sacrificing the sample changer and closing its gap with a Nal-plug, additional factors of
1.5 and
2 can be obtained for compton and natural background respectively.