Chromium is a naturally occurring heavy metal found commonly in the environment in trivalent Cr(III) and hexavalent Cr(VI) forms. Cr(VI) compounds are rated as potential carcinogens. The study covered an analysis of the effect of Cr(III) as CrCl3 (chromium chloride) and Cr(VI) as CrO3 (chromium oxide) on hematolo- gical parameters of Japanese quail (Coturnix japonica). Chromium was added to food and water ad libitium and the experiment lasted 20 days. Significant differences in values of heterophils and lymphocytes were obtained with the tendency of reducing the number of these blood cells. The surface of erythrocytes, thrombocytes and heterophils was significantly reduced (p<0.05). The lymphocytes surface was significantly reduced (p<0.05) during the application of Cr(VI) and increased (p<0.05) when Cr(III) was administered. Chromium caused su- ppression of the immune system, reduced leucopoiesis and affected on microcytic anaemia development.