The space venture resembles other extreme environmental exploration in many respects. Since the beginning of the space program, social and behavioral scientists have predicted that space crews increasingly will begin to experience the kinds of deviant behaviors seen in other extreme environmental duty settings as mission duration, crew size, and heterogeneity increases. However, there has been a long history of neglect by the nation's space agency of those psychosocial human factors which will play such a vital role in future manned spaceflight. The author argues that this is counterproductive, even dangerous, and that social and behavioral studies must be conducted to generate baseline data regarding dysfunctional acts in extreme environments, including the milieu of the space mission. An obstacle to studying occurrences and frequencies of deviant acts is the absence of a standardized definition of such acts in the extreme environment. Borrowing the sanitized NASA term "off-nominal", which generally refers to a maladaptive action, a preliminary reliability test was conducted among five scientists who work with human interaction in extreme environments. They were asked to rate situations from several actual space and polar expeditions for numbers of off-nominal acts. They were told the object of the exercise was to derive a standardized definition and were not provided with any specific definition of off-nominality. Substantial agreement in their ratings provided reliable information to construct a working definition of off-nominality. Various interactions and behaviors which respondents deemed off-nominal could be subsumed under poor expertise, mental disorder, forms of abuse and interpersonal insensitivity, problems of authority and responsibility, task deficits, poor hygiene and fitness, poor field-base communication, and human error with equipment from violating safety procedures and poor judgment as to its usage.