 
 when infant rhesus monkeys were exposed to lead via the addition of lead acetate ( 0.59 mg / kg body weight ) to their formula or by the consumption of lead particles from lead - based surrogate mothers , they developed symptoms of lead intoxication within 6 weeks . 
 seizures , muscular tremors , and altered social interaction were the predominant changes . 
 visual impairment was also apparent in the more severely affected animals . 
 in the animals showing obvious symptoms lead levels varied between 300 to 500 g/100 ml of blood . even in those animals having blood lead levels below 100 g , hyperactivity and insomnia were observed . when the exposure to lead was eliminated , seizures subsided and visual impairment was reduced ; however , the abnormal social interaction persisted . 
 these animals also experienced a gradual decline in hematocrit and hemoglobin values during the period of examination . 
 liver and kidney biopsies obtained from these lead - exposed animals revealed characteristic intranuclear inclusions . 
 when adolescent and adult monkeys were exposed to doses of lead acetate similar to those employed in the infant experiments , lead levels in excess of 200 g/100 ml of blood were recorded 
 . 
 however , there were no obvious behavioral abnormalities observed . 
 there were , however , numerous lead inclusion bodies in kidney biopsy specimens from these animals . 
 
 these data suggest that , like man , the infant nonhuman primate is much more susceptible to lead intoxication than is the adult . 
 the clinical and behavioral changes recorded in these infant rhesus monkeys suggest their use as an experimental model to evaluate lead intoxication . 
 
 imagesfigure 6 . 
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