Forty-two children with malabsorption disorders, one third of whom were considered to have an atopic constitution were given ovalbumin (OA) orally and the serum concentrations were determined by RIA technique after 2 and 8 hr. Most patients showed peak concentrations 2 hours after OA administration but the concentrations varied widely. The determinations were shown to be influenced by antibodies directed against OA. The serum levels of IgG-antibodies to OA, as estimated by a sepharose protein-A technique, were shown to decrease significantly after administration of OA, possibly indicating the formation of immune complexes. High antibody levels were found in children with coeliac disease and in addition in children who had an atopic constitution. A moderate serum concentration of OA in such cases might be an effect of blocking antibodies and does not exclude the possibility of an increased absorption. The uptake of OA was also studied in six patients with food allergy before and after sodium cromoglycate treatment. A beneficial effect on symptoms at the challenge and also a decreased serum concentration of OA after sodium cromoglycate treatment were found (0.05 < P < 0.1). The results support the view that SCG affects the absorption of food antigens. The OA-absorption test, including estimations of both OA and antibodies to OA is considered a useful model for studies of immunological mechanisms involved in food allergy and gastrointestinal disorders.