Previous studies have identified the effects of Vibrio cholerae and its enterotoxin, choleragen (CT A+B+), on the myoelectric activity of rabbit ileal loops in vivo. The response was defined as the migrating action potential complex, the single ring contraction that propels luminal contents aborad. In this study the same rabbit model is used to assess whether migrating action potential complex activity or fluid output is induced by recombinant strains of V. cholerae that produce no subunit of cholera toxin (CT A-B-) or only by the inactive binding subunit (CT A-B+). Three live strains were studied: El Tor wild-type N16961 (CT A+B+) and recombinant strains CVD106 (CT A-B+) and JBK70 (CT A-B-). Controls received sterile culture broth. Migrating action potential complex frequency in animals inoculated with CT A+B+ was significantly increased compared with that in all other experimental groups (P less than 0.01). Fluid output was also increased in animals inoculated with CT A+B+ compared with fluid output in all other groups (P less than 0.05). Migrating action potential complex frequency and fluid output in rabbits given CT A-B+ or CT A-B- did not differ from activity in controls. How these recombinant strains induce diarrhea is unknown, but the mechanism may involve bacterial colonization or production of an unknown toxin.