A bacterial lysate (OM-85 BV), a preparation of purified bacterial ribosomes (D53) and a placebo were tested for ability to induce the local appearance of specific antibody-containing cells. The three compounds were given orally to 90 children who required tonsillectomy. Surgery was carried out after 1 month of therapy. Frozen-cut sections of each tonsil were tested in indirect immunofluorescence. Cells containing antibodies directed to Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae or Klebsiella pneumoniae were enumerated. Lowest values were noted in the placebo group. Slightly higher numbers were observed after treatment with OM-85 BV, but significant increases were noted only for the elevated numbers of specific antibody-containing cells observed after D53 therapy. Bacterial ribosomal preparations thus contribute efficient induction of specific local immune responses in man.