We previously reported that intestine from rats sensitized to ovalbumin (Ova), using Bordetella pertussis vaccine as adjuvant, demonstrated a rapid secretory response [increase in short-circuit current (Isc)] to Ova upon secondary challenge. Here, we examined the role of pertussis toxin, the active component of the vaccine, in the response. Sensitization of Sprague-Dawley rats by intraperitoneal injection of recombinant wild-type pertussis toxin (wPT) plus Ova enhanced intestinal responses (at day 14: approximately 20-fold for luminal antigen, approximately 2.5-fold for serosal antigen) compared with rats sensitized by injection of Ova alone. In contrast, sensitization with an enzymatically inactive mutant pertussis toxin (mPT, different in two amino acids) produced no significant effect. Ova-specific immunoglobulin (Ig) E and IgG2a antibodies and greater numbers of mucosal mast cells were documented in wPT-sensitized rats. In addition, the Isc response to electrical transmural stimulation of nerves in intestinal preparations was significantly augmented. Neurotoxin inhibited the secretory response to luminal but not serosal antigen. Immunophysiological stimulation by wPT was still evident 8 mo postsensitization. Our studies indicate that pertussis toxin causes long-lasting hypersensitivity to coadministered antigens, involving increased production of reaginic antibodies, hyperplasia of mucosal mast cells, and enhanced neurally mediated uptake of antigen across the intestinal epithelium. These findings suggest a potential role for bacterial products in the development of immunophysiological reactions to ingested antigens.