ment of mental retardation as in the young human. These two facts together suggest that the disrup- tion of brain protein synthesis by high phenylala- mine levels in infants may account for the mental retardation observed later in these children. Much work remains to be done to confi m this possibility. However, it is clear from the review and research described by Waisman that neurochemis- try has the tools that will lead to an understand- ing of - and therefore perhaps control of - these inborn errors of metabolism which otherwise can lead to lifetimes of personal tragedy for the af- fected...