Plasma concentrations of propranolol and practolol were measured in patients with coeliac disease and normal subjects. The mean plasma propranolol concentration in the coeliac patients was higher throughout the period of study, the differences being significant at one, six, and eight hours. The plasma concentration profile of practolol in the coeliacs followed a similar pattern but lagged behind that of the normal subjects. A possible reason for these differences is an alteration in the rate of drug diffusion across the atrophic mucosa of the upper jejunum in coeliac disease. Analysis of the results of the propranolol study suggests that an increase in the rate of absorption combined with saturation of first pass extraction may account for the increased plasma concentrations of unchanged propranolol found in coeliac disease. These abnormalities of drug absorption do not appear to be related to the duration of treatment with a gluten free diet.