Changes in spontaneous motor activity in kindled hooded rats were measured following intracerebroventricular administration of three doses of kynurenic acid (65, 39, and 6.5 micrograms, dissolved in 3.3 microliters isotonic saline). Behavior was measured in the automated Digiscan system on every third day during 13 days of drug administration to assess initial behavioral impairment and the development of tolerance. Activity data were collected beginning 5 min after drug administration for six consecutive 5-min samples. The results revealed a suppressive effect of central administration of kynurenic acid on the pattern of spontaneous locomotor activity and showed the development of behavioral tolerance. Initially, the degree of suppression was dose related, but as tolerance developed group differences were minimized. Most measures returned to predrug levels by day 13 except vertical movement, which remained suppressed in the 65-micrograms group throughout testing. This measure may have been more sensitive to the subtle and long-lasting motor impairments resulting from kynurenic acid.