Ability to learn and retain relatively unfamiliar materials has been shown to be impaired in many clinical syndromes, both organic and functional. The testing of this ability features in some form or other in several clinical tests of intelligence, such as the Wechsler Scale and the Binet, while it is more directly tested in the various memory scales. As is well known, efficiency of learning declines with age, and can be greatly reduced by organic brain damage. There is evidence also, which we shall briefly review, that it can be variably reduced in schizophrenia and in psychoneurosis.