Despite a widespread introduction of immunoprophylaxis, the national scientific literature doesn’t frequently deal with the data containing a detailed description of the morphological state of the immune system’s central and peripheral organs, as well as their immunomorphological rearrangement after the use of vaccines and the effects of immunostimulants. It is also worth noting that such organ of the peripheral immune system as a vermiform appendix was mainly ignored by the domestic scientists. We did not find a detailed description of the morphological changes of the rabbits’ vermiform appendix that occur after the introduction of immunobiological drugs. We conducted the histological studies of the vermiform appendix of rabbits after performing an antigenic stress using the vaccine against streptococcal and staphylococcal infections of animals along with the preventive agent “Pneumo-Pro” separately and combined with Selefer, a selenium-containing immunostimulant. The structural changes in the lymphoid apparatus, as well as in the structural elements of the mucous membrane and submucosal basis were noticed after the use of immunobiological drugs. In particular, an expressed hyperplasia of lymphoid elements develops. The infiltration of plasma by submucosal cells was noted too. An increase in the number of exocrine cysts was also observed. The amount of mucus increases on the surface of the mucous membrane. Development of hyperemia and stasis was noted in blood vessels.