In recent years an increasing number of inherited decreases in man has been identified in which there is an impairment of one or more peroxisomal functions. Sofar 15 different peroxisomal disorders have been identified which can be subdivided into three distinct groups depending upon whether there is a generalized (group A), multiple (group B) or single (group C) loss of peroxisomal functions. In this paper we will briefly describe the functions of peroxisomes in man which are of direct relevance for the peroxisomal disorders known up to now. Based upon the biochemical characteristics of the different peroxisomal disorders, we well describe a straightforward approach for the postnatal identification of patients suspected to suffer from a peroxisomal disorder. Furthermore, a detailed analysis of the biochemical procedures which should be used preferably, is given.