Fourteen patients with ataxia-telangiectasia and 10 relatives were studied. Besides neurological examination, laboratorial investigations as to their immunological condition were carried out. In this study, our attention was attracted to the most frequent and relevant laboratorial data being decreased serum and salivary levels of IgA, decreased rate of blastic transformation of lymphocytes and increased serum levels of alpha-fetoprotein (AFP). On the other hand, no patient showed increased levels of carcinoembryonic antigen (CEA). Our population reported a consanguinity rate of 28.5%.