THE CONCEPT OF DYNAMIC EQUILIBRIUM IS USED TO EXAMINE THE OCCURRENCE OF CHANGE IN A THERAPEUTIC INTERVIEW AND TO PROPOSE A THEORY OF THERAPY. BY ANALYZING THE WORKINGS OF THE PSYCHOSOCIAL SYSTEM THROUGH THE GENERAL SYSTEMS THEORY, IT IS POSSIBLE TO SEE HOW CHANGE OCCURS IN AN INDIVIDUAL FAMILY OR COMMUNITY. APPLIED TO A FAMILY INTERVIEW, THE MODEL INDICATES THAT THE INTERVIEWER PLAYS A DISTURBING ROLE IN ORDER TO RENDER A STABLE SYSTEM UNSTABLE AND TO INDUCE A NEW LEVEL OF STABILITY. IT IS SUGGESTED THAT THE PROCESS OF THERAPY CONSISTS OF A LONG SERIES OF SUCH EQUILIBRIA, DISEQUILIBRIA, AND NEW EQUILIBRIA. TO DETERMINE THE DYNAMIC EQUILIBRIUM OF ANY SOCIAL SYSTEM, THE INITIAL STATE OF THE SYSTEM, THE ADEQUACY OF REGULATORY RESOURCES, THE CONSTANCY OF THE ENVIRONMENT, NATURE, FORCE, RATE, AND SEQUENCE OF DISTURBANCES, AND THE CONSEQUENT LEVEL OF ANXIETY MUST BE ASSESSED. THEN, THE EFFORT REQUIRED TO INDUCE CHANGE MAY BE ESTIMATED. THIS SPEECH WAS PRESENTED AT THE 1967 ANNUAL MEETING OF THE AMERICAN ORTHOPSYCHIATRIC ASSOCIATION, WASHINGTON, D.C., MARCH 21, 1967. REPRINT REQUESTS MAY BE ADDRESSED TO 8201 PONCE DE LEON ROAD, MIAMI, FLORIDA 33143. (NS)