Atrazine is a widely used compound in major food crops in the world. Therefore, humans and animals are at risk of exposure to atrazine. The purpose of this study was to determine whether different concentrations of atrazine affect the immune cell functions of fish. In the study we determined the proliferative ability of T and B lymphocytes. The phagocytes were assayed for extracellular production of reactive oxygen species in the phagocytic respiratory burst. In the in vitro study fish were intoxicated with atrazine at doses of 1, 2.5, 5, 10 µg/ml. The results have shown the modulatory effects of atrazine on the selected functions of immune cells isolated from blood and head kidney of rainbow trout.