Alimentary secretions and fecal extracts were assayed for specific antibody in rabbits actively or passively immunized parenterally against a soluble protein antigen, bovine serum albumin (BSA). In contrast to earlier studies with anti-ovalbumin, circulating anti-BSA was demonstrated to pass readily into the gastrointestinal contents of either the actively or passively immunized animals. These data indicate that at least some of the antibody detectable in intestinal contents can be derived from the blood stream ratherthan from the local gut-associated lymphoid tissue.