OBJECTIVE Recent studies report negligible toxicity of oats in the majority of coeliac disease (CD) patients. It has previously been shown that children with untreated CD have circulating antibodies to oats avenin. In this study we performed serial assessments of anti-avenin antibodies in children under investigation for CD on a gluten-free diet with or without oats. MATERIAL AND METHODS The study involved 116 children, randomized to a standard gluten-free diet or a gluten-free diet supplemented with oats. Sera were obtained from 86 children, 48 in the standard gluten-free group and 38 in the gluten-free oats group, of which 33 consumed at least 10 g of oats daily. IgA and IgG anti-avenin antibodies were monitored at 0, 3, 6 and 12 months. Nitric oxide metabolites were measured in 7 patients, with deviating antibody results. RESULTS There was a significant decrease in anti-avenin antibodies in both groups at the end as compared to the beginning of the study, (p<0.001), but no difference was found between the two groups. IgA titres already declined after 3 months. IgG titres, although significantly decreased, remained high in the majority of patients in both groups. Nitric oxide levels were high in four of the analysed samples. CONCLUSIONS Oats per se, do not seem to produce a humoral immune reaction in children with CD when given in an otherwise gluten-free diet, indicating that the reaction requires gluten challenge. Anti-avenin antibodies were equal in the two study groups, and these findings strengthen the clinical impression that oats can be tolerated by the majority of patients with CD.