Lymphoid cells from human palatine tonsils were identified on tissue sections by membrane or intracellular immunofluorescence (IF) staining. Used in an indirect technique, an anti-IgM and an anti-HTLA (human T lymphocyte antigen) antiserum gave complementary patterns of membrane IF, characteristic of the follicular organization. When serial sections were stained for each of the five classes, immunoglobulin-containing cells from all classes were found. Their relative frequencies were, in decreasing order: IgG: 61.6%; IgA: 17.3%; IgM: 12%; IgE: 7.5%; IgD: 1.6%. These differed from those of the gut-associated lymphoid tissue (IgA greater than IgG greater than IgM) and of the peripheral lymph nodes (IgG greater than IgM greater than IgA), but were close to those of mesenteric nodes. The absence of secretory component in tonsil was an additional difference from gut-associated lymphoid tissue and the relatively high proportion of IgE-containing cells, in the absence of recognized atopy, is another feature in common with mesenteric lymph nodes. Finally, slight differences between these results and those obtained on tonsil cell suspensions suggest that some degree of selection probably occurs during the isolation procedure.