A second generation PACS provides an open architecture allowing a seamless connection to other picture archiving and communication systems (PACS) modules with industrial standards. The open architecture of the UCSF PACS provides the flexibility to use commercial `off-the- shelf' components when needed. This paper describes our experience interfacing a stand-alone commercial ultrasound (US) PACS module to our departmental PACS. US PACS module (Acuson Aegis) links 7 Acuson scanners in 2 buildings. This US PACS module features a network sever with 1.5 GB disk storage used for short-term archiving, with images stored in a compressed format (DICOM compatible). The images must be compressed due to the inherently large size of the full images (640 X 480 X 24 bit/image). The interface consists of a gateway which encodes and decodes US images and related patient data to DICOM standards permitting open communication between the module and the PACS infrastructure over ethernet. The first phase of the implementation is to transmit US images to the departmental PACS optical disk library for long term archiving automatically and to retrieve US images from this archive using workstations in the US module. The second phase is to retrieve selected images acquired by other modalities from the archive for display on the US workstation. The third phase is the integration of a pre-fetch mechanism, initiated by the HIS, that sends archived prior studies of patients with scheduled appointments to the US module. Phase 1 has been completed. US images and reports can be archived and retrieved between the departmental PACS and the US module. Retrieval times for cases are between 45 to 120 seconds depending on the time of day. Performance tests have been taken, and average times for study transfers, average study sizes, and general gateway performance issues have been measured. Phases 2 and 3 will be completed shortly. With open architecture design, the US module and the departmental PACS infrastructure function as an integral image information system.