A familial study of 13 Ashkenasy Jewish patients suffering from torsion dystonia (TD) of various origin, was carried out using clinical observation and determination of serum dopamine-beta-hydroxylase (DBH) activity. None of the following criteria: Jewish origin, dominant trait, slow progression and axial topography are specific for an elevated serum DBH activity. A significantly high serum DBH activity was found in TD patients and their relatives compared with controls, particularly in the childhood onset group. Intravenous injection of 20 mg Metoclopramide (MP) did not change serum DBH activity in 12 patients and 17 relatives. In one patient with symptomatic dystonia and two of her maternal relatives (from different fathers) serum DBH activity increased after i.v. injection of MP. In these three cases the serum DBH activity doubled and tripled. It is suggested that the MP induced elevation of serum DBH activity in relatives of TD patients indicates a genetic disposition.