  A new tool is proposed for finding out the completeness limit in apparent
magnitude of a magnitude-redshift sample. The technique, closely related to the
statistical test proposed by Efron & Petrosian (1992), presents a real
improvement compared to standard completeness tests. Namely, no a priori
assumptions are required concerning the redshift space distribution of the
sources. It means in particular that neither the clustering nor the evolution
of the mean number density of the galaxies do affect the result of the search.
