  The multiplicity function (MF) of groups and clusters of galaxies is
determined using galaxy catalogues extracted from a set of Digitized Palomar
Sky Survey (DPOSS) plates. The two different types of structures (of low and
high richness) were identified using two different algorithms: a modified
version of the van Albada method for groups, and a peak finding algorithm for
larger structures. In a 300 sq. deg. area up to z<0.2, we find 2944 groups and
179 clusters. Our MF covers a wide range of richnesses, from 2 to 200, and the
two MF's derived by the two algorithms match smoothly without the need for
additional conditions or normalisations. The resulting multiplicity function,
of slope alpha= -2.08 +- 0.07, strongly resembles a power law.
