During the last decade, the concept of picture archiving and communication systems (PACS) has evolved and matured to integrate digital image information in a hospital. PACS integrates various imaging devices, database archive systems, and image viewing workstations. One of the most difficult problems for integration is the standardization of communication protocols required to connect devices from different vendors. When the ACR-NEMA standard was announced for communications in digital radiology in 1985, it solved some of the problems for PACS with a hardware interface, a set of software commands, and a consistent set of data formats. However, it has been found to be inadequate for networked PACS environments, not only because of its point-to-point nature and lack of a network layer, but also because of its inflexibility to allow other services and protocols to be added in the future. Based on previous experience, the case is made for a new standard for PACS networks and a suggested approach for new protocol is presented. This paper addresses the development of a new standard for PACS protocol layers and attempts to define the protocols from a layered-systems approach. The basis for the new protocol definition is primarily the International Organization for Standardization/Open Systems Interconnection (ISO/OSI) protocols and the data format portion of ACR-NEMA standard. The scope and rationale of the proposed protocol, background, and relationship to PACS technology are discussed. The proposed PACS protocol covers the protocol service definition and specification for the application, presentation, session, transport, and network layers. The proposed PACS protocol is intended to facilitate the development of PACSs by several vendors capable of interfacing with each other. The new PACS protocols will also support a global PACS environment.