The relationship between biochemical parameters and clinical symptoms in angiokeratoma corporis diffusum universale (Anderson-Fabry's disease) has been studied in an extensive English family. The biochemical parameters measured were alpha-galactosidase activity in urine and in single hair roots and the urinary glycosphingolipid excretion per 24 h. The clinical symptoms evaluated included the occurrence of pain, the prevalence of skin lesions, an abnormal ECG, cornea verticillata and other features. Nine male patients and 13 female carriers were studied. No correlation between biochemical parameters and the severity of the clinical symptoms could be found either in the hemizygotes or in the heterozygotes. The urinary alpha-galactosidase activity in all the heterozygotes lay within the normal range. All the obligate heterozygotes (mothers and daughters of hemizygotes) could be detected by analysis of hair roots. Additional heterozygotes were recognized on the basis of clinical symptoms and hair root analysis.