Primary oral antigen exposure normally induces mucosal immunity and an active suppression of the systemic immune response. Patients with systemic lupus erythematosus (SLE) have increased antibodies to bovine gamma-globulin (BGG), which suggested a possible failure of oral tolerance in SLE. We examined this possibility in murine lupus. NZB/W females were fed BGG or saline and were subsequently immunized ip. Primary and secondary responses were assessed. At 1 month of age the mice tolerized normally in response to feeding with BGG but, at 4 months of age, not only did they not tolerize, the mice fed BGG had a 5- to 7-fold higher response to parenteral immunization than did the saline-fed mice. Control strain mice tolerized normally at both ages (a 5- to 10-fold lower response). Conversely, when fed ovalbumin, NZB/W females tolerized normally at both 1 and 4 months of age, and patients with SLE had normal levels of antibody to this antigen. However, we also found increased levels of antibodies to bovine casein in SLE patients, and found that NZB/W mice failed to orally tolerize with this antigen at either 1 or 4 months of age. Thus, the failure of oral tolerance in the NZB/W mice appears to be antigen specific and age dependent and, at least with respect to these three antigens, appears to parallel the antibody patterns seen in human SLE.