Rats injected once into their Peyer's patches with insoluble precipitates of chicken antibody and antigen produced antibodies to chicken IgG (CGG) of the IgM and IgA classes which rose steeply between days 3 and 5 after injection; IgG antibody was detected later and rose more slowly. The IgA antibody was almost entirely in the bile whilst IgM and IgG were found predominantly in serum. In immunized rats with cannulated bile ducts injected intravenously with radiolabelled CGG on day 5 up to 22% of the injected dose was recovered in the bile in 24 hr; in control rats the maximum recovery was 0.4%. Although the complexes were unstable, intact 125I-CGG (some of it bound to rat IgA and secretory component) was demonstrated in bile collected from immunized rats between 1.5 and 3 hr after injection.