The Radiological Society of North America (RSNA) has sponsored demonstrations of the DICOM Standard. The technical details of the demonstrations were initially defined by the MedPACS section of NEMA beginning in 1992 and in subsequent years by RSNA. The Mallinckrodt Institute of Radiology was awarded a series of contracts by the RSNA to provide Central Test Node (CTN) software at the RSNA annual meetings to help vendors demonstrate interoperability. A goal of the early demonstrations was to have vendors communicate with one implementation of the Standard to minimize the amount of testing that needed to be performed prior to the RSNA Annual Meetings. Now that the Standard is better understood and implementations are more mature, vendors are offering more commercial products that utilize the Standard and which communicate with equipment manufactured by other vendors. The DICOM Standard is a technical specification which defines interfaces between equipment. These interfaces are currently defined for network, point to point and disk media. As a technical specification, the Standard does not tell the reader how to design an implementation nor does it provide insight into the thought process of the writers. This paper describes some of the implementation questions and issues that we have seen while working with the CTN software and vendors during the last four years. Examples of problem areas include application entity titles, generation of DICOM unique identifiers and queries for the query/retrieve service classes. The DICOM Standard defines the message formats for association negotiation and exchange of data across the network but provides flexibility in how these messages are used. A specific example is that an application is allowed to propose every service class defined by the Standard when requesting an association but may choose to exchange messages using only one service class once the association is established (for example, storage of CR data). We captured messages sent by vendor applications to the CTN during the 1995 RSNA DICOM demonstration. This paper will discuss some of the ways that vendors have chosen to propose associations and how they utilized the Standard to perform query/retrieve operations.