Behavioural effects were assessed in both young and old rats of the pyridine derivative pyrithioxin, which has been reported to elevate acetylcholine levels in several brain regions in old rats. Pyrithioxin was administered in rats' food according to two separate dosing regimens (200 and 600 mg kg( -1)) over a 6 week period. Spontaneous locomotor activity was measured weekly in photocell cages. Two measures of memory were used: one trial step-down passive avoidance, and spatial learning and retention in the Morris water maze. Pyrithioxin had no effect on locomotor activity or swim speed, but enhanced one trial passive avoidance retention in both young and old animals. The drug also enhanced sensitivity to foot shock and retention of the water maze in old animals.