This study aims to investigate the effects of indoleacetic acid (IAA) and kinetin (Kill, which are plant growth regulators (PGRs), oil antioxidant defense systems [reduced glutathione (GSH), glutathione-S-transferase (GST), catalase (CAT)], and lipid peroxidation level (malondialdehyde, MDA) various tissues of rats. Rats (Sprague-Dawley albino) were exposed to 100 ppm IAA and Kn. One hundred parts per million of PGRs was administered orally to rats ad libitum for 21 days continuously. The PGRs treatments caused different effects oil the content of MDA and antioxidant defense system in comparison to those of control rats. According to the results, the subchronic treatments of IAA caused significant decrease in the GSH concentration and CAT activity in erythrocyte. Kn decreased GSH concentration in erythrocyte too. While the MDA concentration in brain was increased significantly by IAA and Kn, Kn decreased significantly brain CAT and GST activity. The liver GST activity was decreased by IAA and Kn. But, liver CAT activity was increased by IAA. On the other hand, while IAA treatment caused a significant decrease kidney GST activity, Kn caused a significant decrease both kidney GST and CAT activity. Also, while heart CAT activity was decreased by IAA, heart GST activity was decreased by both IAA and Kn. Moreover, MDA concentration in heart was increased by Kn treatment. It was concluded that IAA might effect MDA and antioxidant defense on the animals at subchronic treatment. (c) 2005 Elsevier Inc. All rights reserved.