Anapsos is a medical prescription registered in the Health Ministry of Spain, that is obtained from the rhizomes of the fern Polypodium leucotomos. An immunomodulating effect of Anapsos on certain lymphocyte subsets and cytokines has already been described in the literature. The current study extends and supports part of the aforementioned results of the product on the immune system, showing the ability of Anapsos to stimulate proliferation and activation of T and natural killer lymphocytes, as well as an important down-regulating effect on CD11, CD18 and CD62-L adhesion molecules, both on peripheral blood mononuclear cells and on U-937 and HL-60 cell lines.