The literature involving the use of flooding procedures to achieve fear reduction in both human and infra-human Ss is critically reviewed with reference to techniques, important parameters and theoretical explanations. Much of the research has produced variable and conflicting results due to poor experimental control and confounding, yielding difficulties in interpretation. The following representative conclusions are suggested: (a) stimulus flooding, appropriately administered, appears an effective method of fear reduction; ( b ) the theoretical importance of hypothesized sequential cues is questioned on the basis that the construct serves as neither an explanatory nor a predictive vehicle; (c) parameters accounting for change are not well delineated, but duration of the flooding scene, the quality of its aversiveness to S, and S's initial degree of avoidance behavior appear important; ( d ) extinction as an explanatory principle is seriously overused and alternative constructs from adaptation level theory, modeling theory, and cognitive rehearsal may be involved. Innovative modifications suggest new and interesting research on elicitation of affect and interpretation.