The objective of the study was to investigate the activity of the ethyl acetate (EA) fraction of Euphorbia royleana latex on cellular and humoral-mediated immune responses and phagocytic function of the cells of the reticuloendothelial system in mice. Oral administration of EA at doses of 50, 100 and 200 mg/kg p.o. in mice with sheep red blood cells (SRBC) as an antigen-inhibited both the delayed-type hypersensitivity reaction and the production of circulating antibody titre. Reduction of CD4+ T cell counts in the peripheral whole blood and the neutrophil counts in pleural exudates of the animals treated with EA was observed by flowcytometric analysis. Process of phagocytosis was also inhibited in in vivo and in vitro experimental test models. The oral LD50 in both rats and mice was more than 2.5 g/kg body weight.