A total of 59 relatives of patients suffering from Cuban Dominant Cerebellar Ataxia (SCA2) were studied, undergoing physical examination in order to evaluate them clinically as well as by studies of peripheral nerve conduction. Clinical manifestations were detected in 13 of these patients. In 11 other patients there were electrophysiological alterations without symptoms or signs. The main electrophysiological alterations detected were reduced amplitude of the sensitive potentials. This is an expression of an axonal lesion occurring at a presymptomatic stage.