Sprague-Dawley rats (ages 1 to 21 days, alternate days) were chosen for study. Animals were injected with methylmercuric chloride (8 mg/kg IP); 12 hr later each animal was injected with uniformly labeled L-(14C)leucine, allowed 30 min for incorporation, and decapitated. Brains were analyzed for amounts of radioactivity incorporated into TCA precipitable protein. When compared to baseline curves for control animals, curves of treated animals were compressed overall and had age-dependent increases and decreases in rates of protein synthesis.