In previous researches some of the Authors proved that Zymosan acts as adjuvant in determining the experimental autoimmune aspermatogenesis, in absence of skin reactivity of delayed type. The aim of the present investigations was to ascertain if Zymosan possess some components analogous to those of mycobacteria, which can be considered responsible in determining hypersensitivity reactions of delayed type. The results, obtained also in cross experiments, don't confirm this hypothesis.