The move towards the use of object-oriented methods for information system development has led to the need for object-oriented approaches to requirements engineering. Research into current system development practices in object-oriented requirements specification is necessary for techniques and tools to evolve and improve. This paper describes a set of four case studies that examined the use of object-oriented methodologies in professional requirements engineering practice by experienced system developers. In these studies, it was found that the widely published and commonly available methodologies were rarely used in their entirety, if they were used at all. Rather, most consultants interviewed developed in-house methodologies based on selected parts of methodologies and notations described in the literature and their own experience of “what had worked for them in the past”. The reasons for this development of in-house methodologies include cost constraints for commercial methodologies and personal preference for the flexibility in adapting parts of methodologies to suit a specific task or project. This research project confirms and extends the findings of existing research in the use of system development methodologies and in particular, contributes to research into both requirements definition and object-oriented development practice.