The success of the Object Management Group's General Inter-ORE Protocol (GIOP) is leading to the desire to deploy GIOP in an ever-wider range of application areas, many of which are significantly more demanding than traditional areas in terms of performance. The well-known performance limitations of present day GIOP-based object request brokers (ORBs) are therefore increasingly being seen as a problem. To help address this problem, this paper discusses a GIOP implementation which has high performance and quality of service support as explicit goals. The implementation, which is embedded in a research ORE called GOPI, is modular and extensible in nature and includes novel optimization techniques which should be separately portable to other ORE environments. This paper focuses on the message protocol aspects of GOPI's GIOP implementation; higher layer issues such as marshalling and operation demultiplexing are not covered in detail. Figures are provided which position GOPI's GIOP performance against comparable ORBs. The paper also discusses some of the design decisions that have been made in the development of the GIOP protocol in the light of our implementation experience.