Energy drinks have become popularized and the market value for these drinks is continually growing. Therefore, the present study aimed to evaluate the effect of three popular kinds of energy drinks (Power Horse, Red Bull and Code Red) on certain hematological parameters and on the ultrastructure of blood cells in male Wistar albino rats. Animals were treated orally with Power Horse, Red Bull and Code Red respectively for 4 weeks. Blood samples were taken after two and four weeks for determination of haematological indices. Ultrastructure examination of blood cells was carried only after 4 weeks of treatment. The results indicated significant reduction (P