The systems theory concept of the closed system is suggested by Ronald Fairbairn as one metaphor both for internal object relationships, and their expression in transference. This paper considers how this metaphor may be helpful in analysing the patient-therapist relationship and, particularly, in deciding when aspects of it should be understood as transference. The argument is that one major challenge could be seen as lying in the complexity and subtlety of internal world systems, and a second in the many factors that conspire to lure the therapist to participate in rather than notice them. The systems metaphor seems useful both in bringing into focus some of the difficulties in analysing the therapist-patient relationship and also in offering a vehicle for thinking about them.