The differentiation in the clinical setting of psychoanalysis be tween the manifestations of delusions and the reporting of primitive perceptions would seem to be an area of observation and description opened up by Bion's Theory of Thinking. By offering us a model that enables us to conceive of such a differentiation he has made possible our monitoring the phenomena of our consulting room for their realizations. The theory of alpha-function and beta-elements has already proved itself fruitful for clinical observation in the area of communication of meaningful messages versus communication-like missiles of meaningless stuff. In work with psychotic children it has helped us to recognize their response to bombardment with emotional experiences for which they have no capacity either of containment or thought. It also gives us a basis for distinguishing between immaturity and psychosis.