Single administration of aldrin (2-10 mg/kg) to adult male albino rats (120-130 g) enhanced locomotor activity (LA), with the maximum effect reached 2 h after treatment. The measurement of steady state levels of glutamate, glutamine and the activities of their metabolizing enzymes in different regions of the brains of rats treated with aldrin under its nontolerant condition showed that aldrin enhanced the activity of the neuronal glutamate system in the cerebral cortex, cerebellum and hypothalamus. Moreover, treatment with the glumatergic NMDA receptor antagonist D,L-2-amino-7-phosphonoheptanoic acid, in the absence and presence of aldrin, reduced the LA of control rats and attenuated the aldrin-induced increase in LA of treated rats. These results suggest that aldrin-induced activation of the central glutamate system may be a cause of stimulation of LA with aldrin under its nontolerant condition. © 2001 Prous Science. All rights reserved.