EN
This is a review article concerning an influence of trematodes infections on a defence system of snails. Changes in: snails' plasma composition, a number of hemocytes, size of a hemo-poietic organ, molecules secreted by hemocytes and defence cells activities caused by the infections are discussed in detail. The differences in humoral and cellular response between susceptible and resistant strains of snails as well as between young and old snails are also presented in the article. Finally, the problem of an existence of the specific immunological memory in snails is analyzed.