Appraisal of gut lavage in the study of intestinal humoral immunity. Direct investigation of intestinal humoral immunity requires collection of intestinal secretions or mucosal biopsy specimens, or both. A non-invasive technique of gut lavage, with a polyethyleneglycol electrolyte lavage solution as a means of collecting intestinal secretions for immunoglobulin and antibody studies, was evaluated. Fifty patients were studied--25 immunologically normal patients or volunteers, 15 patients with untreated coeliac disease, and 10 patients with active Crohn's disease. Protease inhibitors were added promptly to samples to prevent proteolysis of immunoglobulin content. Treated lavage samples were assayed by enzyme linked immunosorbent assay for immunoglobulin and antibody content. Studies of serial lavage specimens showed that early, faecally contaminated specimens contained negligible quantities of immunoglobulin, but once the specimens became clear a steady state was reached, with little variation in immunoglobulin content between serial specimens and with a uniform dilution (around 20%) of the ingested polyethyleneglycol. Gut lavage fluid IgA was predominantly secretory, comprising 92%, 81.6%, and 76.7% respectively of the total IgA gut lavage fluid content in the control, coeliac, and Crohn's groups. High values of total IgM and IgA and IgM antigliadin antibodies were detected in the coeliac group, and high values of IgG in the Crohn's disease group. This method of gut lavage is not only an effective bowel cleanser, but also a noninvasive means of obtaining intestinal secretions for the study of humoral immunity in gastrointestinal disease. 