A single oral or intramuscular immunization with purified cholera B subunit induced an intestinal secretory immunoglobulin A (IgA) antitoxin response in, respectively, 10 out of 11 and 9 out of 12 Bangladeshi volunteers. The IgA titre rise in intestinal lavage fluid was similar by either route of immunization, but the duration of the response was usually longer after the oral dose. A second immunization by either route, given 25 days after the first, and a third dose (oral only), given 15 months later, resulted in intestinal immune responses which did not differ in magnitude from that induced by the initial immunization but were observed significantly earlier, usually by day 3. Both the first oral and intramuscular immunizations induced significant antitoxin titre rises, mainly IgG, in the serum in most vaccinees but the magnitude of the response was considerably higher after the intramuscular dose. Significant IgA antitoxin titre rises in saliva and breast milk were seen after both oral and intramuscular immunization.