Two patients with cystic fibrosis (CF) who subsequently developed celiac disease (CD) are described. Since organ culture of intestinal mucosa has been used to establish an in vitro model for the study of CD, we utilized this opportunity to determine whether duodenal mucosa obtained from each of these two patients and their immediate families differed in its organ culture behavior from mucosa obtained from patients with CD alone. Additionally, as specific HL-A types are associated with CD, we used HL-A typing to determine whether the two patients with CF-CD differed genetically from patients with CD alone. One of our patients was HL-A8, the most common type associated with CD; the other was HL-A12, as are many of the non-HL-A8 celiac patients. The response in organ culture of the mucosa of these two patients was the same as the response in organ culture of the mucosa from patients with CD alone. These and other data suggest that CD occurring in patients with CF is no different than CD occurring alone.