There is a substantial literature on the organisational responses of hospitals to contemporary challenges but there is much less written about workable arrangements at a departmental level. An opportunity to change service delivery by a teaching hospital psychiatry department occurred as a result of the chance occurrence of a number of factors that were not fully appreciated by the staff at the time. This paper describes the challenges involved in merging two previously separate organisations to form a single integrated mental health service. This necessitated a change in the way clinical programmes were delivered and a new management structure. Planning and implementation were interactive rather than sequential processes and, at times, were chaotic. Resistance became widespread as difficulties emerged with the loss of many consultants and completion of the plan was due to the ongoing commitment of the remaining staff and support from the hospital managers, and owed something to good fortune. In the middle of the process there were times when it appeared that many things had been made worse and it was tempting to delay or even abandon key reforms. Retrospectively, many of the factors that have been reported to be associated with successful change management strategies were present, but given that this amalgamation was of two relatively small organisations (total budget $6.5 million and staff approximately 100 full-time equivalents in 1996), it reinforces the view that major change cannot successfully happen within a professional organisation unless strongly supported and 'owned' by the key staff who will have to carry it through and deal with the consequences. This has major implications for those who would attempt to impose such change from outside.