Despite considerable cajoling and some good results, behavioural psychotherapists have remained predominantly intra-personal in the focus of their research. Analysis of the wider environmental determinants of the behaviours that concern them have been few, and there has been no upwards trend. This is problematic in that it fails to exploit the full scope of behaviourism, limiting practitioners and their efficiency. The present analysis concerns one kind of systems-level work, the use of data to guide a psychiatric day hospital service. Although limited in rigour and scope, it nonetheless indicates a ready and promising “generalization” of behaviour therapy from the individual to the system. The study also illustrates how the emerging behavioural assessment principle of “treatment utility” can be analysed.