The relative distribution of IgA and IgG subclass-producing immunocytes was examined by two-colour immunohistochemistry in normal human distal ileum including Peyer's patches (PP), regional mesenteric lymph nodes (MLN), and peripheral lymph nodes. IgA2 cells predominated slightly over IgA1 cells in the PP dome area. There was a decreasing median proportion of IgA2 cells in the order of PP (52%), distant ileal lamina propria (40%), MLN (32%), and peripheral lymph nodes (11%). The reverse was true for IgA1 cells in independent enumerations. These results support the notion that PP-derived B cells after stimulation are seeded mainly to the lamina propria of the distal gut, but that there is a substantial retention and terminal differentiation of this migrating population in regional MLN. The median subclass proportions of IgG-producing cells in the PP dome area were in independent determinations 68% IgG1, 23% IgG2, 8% IgG3, and 9% IgG4. This distribution was fairly similar to that seen in other tissue categories, except for a trend towards increased IgG1 and reduced IgG2 proportions in peripheral lymph nodes and reduced IgG1 along with increased IgG3 in normal palatine tonsils. The data suggested an association between the expression of IgG2 (and possibly IgG4) and IgA2 in intestinal mucosal immune responses.