Obvious or overt malnutrition is diagnosed from characteristic clinical signs. Subclinical malnutrition is revealed only by biochemical changes but is an unstable state which, if untreated, will develop to clinical malnutrition. There appears to be a stable state where the subject has adapted to low levels of nutrient intake for which the name 'covert malnutrition' is suggested. Examples are: (1) vitamin C intake of 10 mg per day which is adequate to prevent scurvy and where no clinical signs appear until the stress of wounding is applied to the tissues; (2) inadequate intake of vitamin A without signs of deficiency because the poor diet limits growth--deficiency shows up when growth is resumed: (3) protein intake which is adequate to maintain N balance but not adequate to withstand stress. All dietary surveys reveal apparently healthy individuals whose intake of nutrients appears to be grossly inadequate--these may be 'suffering' covert malnutrition, although there is no evidence to indicate whether or not this stable condition is harmful.