The immunomodulating capacities of dimethylglycine (DMG) were examined in a rabbit model. Female New Zealand white rabbits were immunized on day 0 and were given booster inoculations on day 9 with either killed influenza virus or Salmonella typhi vaccine. Experimental animals were force fed 20 mg/kg body weight of DMG daily beginning 14 days prior to the first inoculation and continuing throughout the experiment. Control animals were force fed daily only distilled water. Blood was obtained on day 0, day 9, and day 30. Hemagglutination inhibition assays showed a more than fourfold increase in mean antibody titer to influenza antigen in the DMG-treated animals (p = 0.0006) after the first inoculation, and a fourfold increase in mean titer after the booster inoculation (p = 0.1000). A standard agglutination test for Salmonella typhi O (somatic) and H (flagella) antigens was performed on all sera from animals receiving the typhoid vaccine. Mean antibody titers to the O antigen were significantly higher (more than threefold) after the first inoculation (p = 0.0302) and more than fivefold higher after the booster inoculation (p = 0.0047) in DMG-treated animals. Mean antibody titers to the H antigen were also higher in DMG-treated animals compared with controls after both the first and second inoculation. Lymphocyte transformation assays on cells taken from DMG-treated animals immunized with the influenza vaccine showed a tenfold increase in mean proliferative response (p = 0.0024). Lymphocytes from DMG-treated animals immunized with the typhoid vaccine showed a fourfold increase (mean values) in thymidine uptake (p = 0.0180). No toxicity or adverse effects were observed at any time during the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)