Plasma levels of thyrotrophin before and after the intravenous administration of 200 microgram of thyrotrophin releasing hormone have been studied in eleven patients with active gluten-induced enteropathy and in a group of twenty-one normal prepubertal children. In nine out of eleven coeliac patients an exaggerated and/or sustained response of plasma thyrotrophin is observed. Basal plasma thyrotrophin level is not significantly different from the value observed in normal children. However, plasma levels recorded 20 and 60 min after injection of the releasing hormone are significantly higher than in control children (at 20 min: P less than 0.01; at 60 min: P less than 0.001). Serum levels of dialysed triiodothyronine and thyroxine and of triiodothyronine are significantly lower in coeliac patients than in normal infants (P less than 0.01). These data support the evidence of an endocrine dysfunction in coeliac disease. It is not clear whether it is due to malnutrition and/or to some direct action of circulating gluten-peptides on the hypothalamus.