Mallard ducks were dosed with a single shotgun pellet (ca. 200 mg lead). After 1 month there was about 1 ppm lead in blood, 2.5 in liver, and 0.5 in brain. Lead-induced inhibition of delta-aminolevulinic acid dehydratase enzyme in blood and cerebellum was much greater than in cerebral hemisphere or liver and was strongly correlated with the lead concentration in these tissues. The cerebellar portion of the brain was more sensitive to delta-aminolevulinic acid dehydratase enzyme inhibition by lead than were the other tissues examined. There was also a greater increase in the glial cell marker enzyme, butyrylcholinesterase, in cerebellum than in cerebral hemisphere, suggesting that nonregenerating neuronal cells were destroyed by lead and replaced by glial cells in that portion of the brain. Even partial loss of cerebellar tissue is severely debilitating in waterfowl, because functions critical to survival such as visual, auditory, motor, and reflex responses are integrated at this brain center.