Epidemiological as well as animal studies have shown that environmental factors such as nutrition contribute to the development of diabetes. In this study we investigated whether the early introduction of a gluten-free diet can influence the onset and/or incidence of diabetes, as well as insulitis and the number of gut mucosal lymphocytes, in non-obese diabetic (NOD) mice. Gluten-free and standard Altromin diets (with the same milk protein and vitamin content) were given to breeding pairs of NOD mice as well as to the first generation of NOD female mice, which were then observed for 320 days. A substantially lower diabetes incidence (chi(2)=15.8, p=0.00007) was observed in NOD mice on the gluten-free diet (15%, n=27) compared to mice on the standard diet (64%, n=28). In addition, mice on the gluten-free diet developed diabetes significantly later (244+/-24 days SEM) compared to those on the standard diet (197+/-8 days, p=0.03). No differences in the number of CD3(+), TCR-gammadelta(+), IgA(+), and IgM(+) cells in the small intestine were observed. We showed that gluten-free diet both delayed and to a large extent prevented diabetes in NOD mice that have never been exposed to gluten. Copyright 1999 John Wiley & Sons, Ltd.