OBJECTIVE In first-degree relatives of celiac patients, the risk of oligosymptomatic celiac disease is elevated. These individuals therefore also have a higher potential for malignancy or nutritional deficiencies. Lactulose/mannitol permeability is increased in untreated celiac patients and has been recommended to screen for celiac disease. We investigated the usefulness of a lactulose/mannitol home test kit for screening first-degree relatives home test kit for screening first-degree relatives of celiac patients. METHODS The lactulose/mannitol test was performed at home by 111 first-degree relatives. These subjects received the test kit from celiac index patients, were instructed by an information sheet how to carry out the test, and were asked about their symptoms by questionnaire. When lactulose/mannitol permeability was abnormal, endomysial antibodies were tested by immunofluorescence. Any relatives with positive endomysial antibodies were then biopsied. To investigate the specificity of the lactulose/mannitol test for celiac disease, 40 patients with nonspecific gastrointestinal symptoms were tested. RESULTS Lactulose/mannitol permeability was elevated in 34 (31%) relatives, but only nine (8%) of those relatives showed positive endomysial antibodies. Flat mucosa was found in all nine relatives after biopsy. The prevalence of celiac disease was much higher (42%) among 12 relatives who contacted the outpatient clinic themselves because of symptoms. Seventy-one percent of the remaining 21 relatives with elevated permeability demonstrated normal intestinal permeability at a control test within 1 yr. CONCLUSIONS By combining the lactulose/mannitol test with endomysial antibody testing, we have developed a good strategy for use in screening for celiac disease among first-degree relatives.