ABSTRACTThe effects of different concentrations of 20-hydroxyecdysone (20-E) on hemocytes of Galleria mellonella were investigated in vitro. Hemocyte culture was performed in Grace's insect medium with fetal calf serum. The hormone was added to the cultures at two different concentrations. During a period of three days, the cells (plasmatocytes, granulocytes and total cell number) were counted under an inverted microscope. Obtained numbers were evaluated with one way variance analysis (ANOVA). Hormone treatment led to a dose-dependent decrease in total cell and granulocyte number. The number of plasmatocytes, which are the predominant cells for phagocytose activity in immune response, was enhanced by hormone treatment. Key Words: 20-hydroxyecdysone, hemocyte, in vitro, Galleria mellonella, insect