BACKGROUND: The main objective of the study was to assess the frequency of undetected coeliac disease among the first-degree relatives of families with two or more previously diagnosed coeliac disease patients. The value of the serum endomysial antibody test as a single means of detecting clinically silent coeliac disease was evaluated. The correlation of endomysial and tissue transglutaminase antibodies and the correlation of endomysial antibodies to the HLA typical for coeliac disease was determined. METHODS: A total of 137 multiple-case coeliac disease families with 872 family members were recruited; 466 healthy family members were simultaneously screened for gliadin and endomysial antibodies and thereafter for tissue tranglutaminase antibodies. Antibody-positive persons were typed for HLA-DQ2 and DQ8. The diagnosis of coeliac disease was based on the typical mucosal lesion on small-bowel biopsies. RESULTS: Forty-four (9.4%) of the healthy family members were positive for endomysial and 48 (10.3%) for gliadin antibodies; 42 biopsies revealed 29 new coeliac disease patients (6.2% of healthy individuals). Endomysial antibodies detected 97% and gliadin antibodies 52% of the new cases. All 44 endomysial-antibody-positive and 35 of 48 gliadin-antibody-positive individuals were positive for DQ2. Tissue transglutaminase antibodies corresponded well with endomysial antibodies. CONCLUSIONS: Undetected coeliac disease is common even among healthy first-degree relatives of multiple case families. The findings emphasize the value of serum endomysial antibodies in the detection of clinically silent coeliac disease. Endomysial-antibody-positive individuals, unlike gliadin-antibody-positive ones, share the coeliac disease-type HLA-DQ.