Stimulus barrier may be reformulated as a complex ego function measurable along a dimension of adaptiveness–maladaptiveness. It refers to those structures and functions which enable a person to regulate amounts of inner and outer stimulation so as to maintain optimal homeostasis and adaptation. The 'receptive' and 'protective' functions referred to by Freud have been elaborated here to include both sensory thresholds and also the organization of sensory experience. Together, these 'component factors' of stimulus barrier as an ego function have been organized and developed into a rating scale keyed to interview questions (see Appendix). These scales have been used to rate data from clinical interviews and, along with similarly constructed scales for 11 other ego functions, may be useful in determining the relationship of stimulus barrier to other ego functions and in determining its place in the hierarchy of ego functions.