The aim of the study was to determine the stimulating effect of a natural immunostimulator – dried brewer’s yeast (Saccharomyces cerevisiae) – on specific and non-specific humoral and cellular immunity of the offspring of ewes fed a diet supplemented with Saccharomyces cerevisiae yeast during pregnancy or lactation. The study involved 66 lambs from ewes divided into 3 groups: I – control group fed a diet not supplemented with yeast, II – experimental group fed a diet containing dried brewer’s yeast (Saccharomyces cerevisiae) since the 4th month of pregnancy, and III – experimental group fed a diet with the addition of yeast since lambing. From 28, 56 and 70 days old lambs blood was sampled from the jugular vein to determine the indicators of specific and non-specific humoral and cellular immunity (gamma globulin content, lysozyme activity, ceruloplasmin activity, total protein content and MTT assay of lymphocyte proliferation after stimulation with ConA or LPS, respiratory burst activity of phagocytes – RBA, potential killing activity of phagocytes – PKA). The obtained results are indicative of the immunomodulating properties of dried brewer’s yeast (Saccharomyces cerevisiae) in the offspring of ewes fed a diet supplemented with yeast from the time of lambing or from the 4th month of pregnancy.