A new method for determining the two-dimensional number density profile in groups and clusters of galaxies is presented and tested. It is based on the use of the distribution of intergalactic projected separations, which can be calculated in a straightforward manner from the positions of galaxies in a plate. After establishing the mathematical foundation and practical implementation of the method, we show its potential by applying it to Monte Carlo clusters with a small number of galaxies. Several questions of interest to the general user are discussed and illustrated with real data. With this new method, reliable number density profiles can be determined for groups and clusters with a small number of galaxies.