There are now ten known heritable disorders of lipid metabolism for which the nature of the underlying enzymological defect is conclusively established. In addition to devising procedures for successful enzyme replacement therapy, much current work deals with the development of convenient, effective methods for the rapid diagnosis of patients with these disorders, the detection of heterozygous carriers of these diseases, and the monitoring of pregnancies at risk for these conditions. Clinical enzymologists are required to assume increasing responsibilities in the performance of these tests, and the present contribution describes the application of fundamental principles and discusses recent developments along this line. In particular, the development of facile chromogenic reagents for the diagnosis of patients with Niemann-Pick disease and Krabbe's disease is delineated. Previously, the diagnosis of such patients required the use of radioactivity labeled compounds and such testing was limited to relatively few research laboratories. The novelty of these reagents and their application comprise the major aspect of this presentation.