One purpose of clinical neurochemistry has been to indicate "activities" of catecholamine systems, by assaying levels of the effector compounds or their metabolites in body fluids such as plasma, cerebrospinal fluid, urine, or microdialysate. This review discusses a new purpose: relating specific catecholaminergic phenotypes to neurogenetic disorders. Distinctive catecholamine patterns in several neurogenetic conditions reflect enzyme deficiencies as direct or indirect effects of gene mutations. These neurochemical patterns can provide potentially important clues to the diagnosis, treatment, and pathophysiology of neurogenetic disorders. Linking genetic abnormalities with molecular mechanisms and clinical manifestations of disease represents a useful new direction in clinical neurochemistry.