That symptomatic celiac disease (CD) can occur in several members of a family has long been recognized. Given the possible complications of untreated CD, it is also important to diagnose those family members with "silent" disease, to offer them the benefit of a gluten-free diet. We studied 642 first-degree relatives of 210 patients with CD, two of the latter belonging to the same family. IgA and IgG antigliadin antibodies and IgA antiendomysium antibodies were studied in all. Jejunal biopsy was performed in 59 subjects, 47 with positive and 12 with negative serological markers. Celiac disease was diagnosed de novo in 18 cases (2.8%). Diagnosis in a symptomatic mother was made by jejunal biopsy despite the negativity of all immunological markers. We conclude that the risk of having CD is higher in siblings than in parents of patients with CD, that the most useful marker for diagnosis is the study of IgA antiendomysium antibodies, and that the absence of positive serological markers does not completely exclude the diagnosis of CD.