This paper outlines some of the theoretical principles underpinning the psychotherapeutic treatment of íbrderline patients in a day-hospital setting. The main emphasis is on maintaining a creatively functioning parental couple in different contexts. The parental couple is conceptualised as a balance of appropriate ‘doing’ and ‘being’. The attacks of the borderline patient, through splitting and projective identification, on the creatively functioning parental couple leads to excessive ‘doing to’ or inappropriate ‘being with’ on the part of the staff. The different contexts in which the parental couple is attacked are described. The task of the day hospital and the staff group is to hold the parental couple in mind at all times and to function as a cohesive whole. In order to do this the day-hospital functions as a transitional space in which ‘doing’ and ‘being’ are explored, especially through the understanding of countertransference reactions. The use of a third object to maintain a therapeutic balance is discussed.