Molecular genetic predictive or prenatal genetic testing is now possible in families with one form of adult-onset, autosomal dominant ataxia (SCA 1). Before the SCA 1 gene was isolated, we began a study of the knowledge of genetics, the perception of the disease, and the intended use of genetic testing among members of two large SCA 1 kindreds. Questionnaires were sent to 210 consenting affected, at-risk, and spouse members of two SCA 1 kindreds; data from the 117 respondents were analyzed on a personal computer. Sixty-nine percent of respondents thought predictive testing (by genetic linkage) should be made available immediately, and 42% thought prenatal testing should be made available. The kindreds differed in several important aspects: knowledge of genetic concepts, family size, and anticipated emotional responses to genetic testing. No respondent had obtained individualized genetic counseling. There is moderate interest in genetic testing for this fatal neurodegenerative disease of adulthood. Members of our kindreds have not received genetic counseling outside of the research setting. Finally, factors specific to a particular kindred may influence or predict individual responses to genetic testing.