The study comprised 25 children suffering from PEM. Ten of them were non-oedematous and the rest were oedematous. A group of 10 children of similar age served as the controls. A state of hyperammonaemia with slightly reduced blood urea was found in both forms of PEM but was more marked in kwashiorkor. There was also a highly significant increase in CSF ammonia in all cases of PEM studied. Some of the mental changes which have been observed in kwashiorkor may be, at least in part, due to ammonia intoxication.