Gut mucosal, salivary and serum antibody responses to a new oral cholera vaccine, consisting of B subunit and whole cell vaccine (WCV), were studied in Swedish volunteers. A single immunization with a 0.5 mg dose of B subunit together with WCV (5 X 10(10) killed cholera vibrios) induced a local intestinal immunoglobulin A (IgA) antitoxin response in 4/6 (67%) vaccine recipients as evident from specific antibody titre rises in intestinal lavage fluid. A second administration of vaccine did not further enhance the intestinal immune response beyond the peak level induced by the initial immunization. Different doses of B subunit (2.5 and 0.5 mg) given together with 5 X 10(10) killed vibrios (WCV) induced antitoxin antibody responses in serum in about the same frequency, 10/13 (77%) responders versus 13/14 (93%), as well as in saliva, 7/13 (54%) versus 9/14 (64%), and a single immunization was almost as efficient as two vaccine administrations. Single or repeated oral vaccination only irregularly resulted in modest antibacterial titre rises in serum (9/27 = 33%) or saliva (12/27 = 44%), but stimulated a significant mucosal antibacterial response in intestine of 5/6 (83%) examined volunteers.