Celiac disease is a chronic illness of the small bowel caused by gliadin intolerance in genetically predisposed subjects. The aim of this study was to investigate serum levels of IgA and IgG antigliadin antibodies, IgA antiendomysial antibodies, and IgA anti-tissue transglutaminase antibodies in 169 patients with autoimmune thyroid diseases, i.e. chronic thyroiditis and Graves' disease. Antiendomysial antibodies were positive in 2 out of 169 persons (1.18%), IgA antigliadin antibodies in 15.98%, IgG antigliadin antibodies in 51.48%, and IgA anti-tissue transglutaminase in 14.79%. The prevalence of positivity was higher compared to the 1312 control blood donors described in our previous study (Vancíková et al. 2002) (p<0.05). Patients with chronic thyroiditis treated with a high replacement dosage of levothyroxin (125-200 microg daily) had higher serum levels of IgA antigliadin antibodies in comparison with patients treated with a lower dosage (50-100 microg daily) (medians: 13.00 vs. 19.69, p=0.033). We found a negative correlation of IgA anti-tissue transglutaminase antibodies and total calcium serum levels (r = -0.480, p=0.0236, n=22). We can conclude that in persons with autoimmune thyropathy there is a high prevalence of positive antigliadin, anti-tissue transglutaminase and antiendomysial antibodies. Latent celiac disease may lead to impaired resorption of therapeutically administered levothyroxine, calcium, or other substances.