The uptake of ovalbumin (OA) from egg and beta-lactoglobulin (BLG) from cow's milk into the blood was investigated for seven hours after a test meal in five children with coeliac disease on a gluten free diet and after gluten challenge, and in five children with normal jejunal mucosa. Ovalbumin was detectable by ELISA in three of five coeliac children (maximal concentrations 8-178 ng/ml serum) and in five of five controls (maximal 4-91 ng/ml serum). Beta-lactoglobulin was detected in three of five coeliac children (maximal 0.6-6 ng/ml serum) and in two of five controls (maximal 0.5 and 50 ng/ml serum). No clear relationship was seen between maximal antigen concentrations and titres of serum IgG or IgA antibodies determined by ELISA, or as percentage antigen binding in a Farr type radioimmunoassay. Ovalbumin and beta-lactoglobulin was seen in serum of all coeliac patients and controls by HPLC fractionation in combination with ELISA, either in high MW fractions, or at the Mr of native OA and BLG, respectively. In one control degradation products (about 17 kD) of BLG were detectable in serum. The serum concentrations of OA and BLG were increased on gluten challenge in four or five coeliac children, indicating increased macromolecular passage through the gut mucosa in untreated coeliac disease.