In an experiment designed to test aspects of the psychoanalytic theory of ego functioning, 18 male and 18 female subjects were assigned in equal numbers to a 3 1/2-hr period of either sensory deprivation (SD), social isolation (SI) or social participation (SP). Their level of autistic thinking was assessed by a word-association measure administered immediately before and immediately after the treatment condition to which each subject had been assigned. Results showed that subjects assigned to SD showed an increase in autistic thinking scores from pretreatment to posttreatment, whereas subjects assigned to the two control conditions (SI and SP) showed a decrease. Although Minnesota Multiphasic Personality Inventory (MMPI) ego strength (Es) scores correlated negatively with the initial level of autistic thinking in all subjects, the experimental and control conditions had their greatest impact on subjects who scored low in Es. Results were interpreted as supporting the hypothesis that consensual functioning (particularly for subjects who scored low on Es) depends on continuing contact with reality.