Many cases of coeliae disease are currently undiagnosed. We carried out a pilot study on screening for coeliae disease in a school population. The screening protocol consisted of three parts: (1) IgG and IgA antigliadin antibody (AGA) assay; (2) antiendomysium antibody and total serum IgA determinations; (3) jejunal biopsy. A total of 5280 students aged 11-15 years (71.7% of the eligible population) underwent the first evaluation; 113 subjects performed the second tests and 35 of these needed the third investigation. Coeliae disease was diagnosed in 23 cases, most of which were atypical or silent forms. The prevalence of undiagnosed coeliae disease was 4.36 per 1000 screened subjects (95% CI 2.58-6.14) and 5.03 per 1000 (95% CI 3.41-6.65) in the general population. The ratio of known to undiagnosed cases was 1 to 6.4. This high prevalence of undiagnosed coeliae disease raises a number of problems that require further evaluation.