Three difficult problems in making picture archiving and communication systems (PACS) a clinical reality in radiology are image archiving, very high-resolution display stations, and high-speed networking. This paper considers high-speed image transmission through a high- capacity network. Several commercially available high-speed networks were tested over the past year. Only one of these networks (UltraNet) has adequate throughput and capacity potential necessary for the PACS used in the test. The focus of this experiment is to determine the throughput and capacity characteristics of this star topology networking scheme as relates to the operation of a PACS in the clinical environment. A large-scale test was performed to gauge network memory-to-memory performance for three networking configurations modeling those in a PACS: duplex, parallel and relay. Ten computers used in the PACS (Sun 3 and 4 class computers) were connected with UltraNet for the test. For point-to-point throughput (half-duplex model) the network delivers up to 3.1 megabytes/second (MBps) for Sun 3/computers and 4.7 MBps for the Sun SparcServer 490. As regards capacity considerations (parallel model), five parallel image transfer processes generated a maximum of 13.9 MBps through the network. Only a slight degradation in individual process throughput was observed (1.4%). With regard to shared access to high-contention resources on the PACS network (e.g., archive servers), this network demonstrated equal sharing of server networking capacity between various client computers (relay model). For disk-to-disk performance measurement under loaded clinical conditions between two SparcServer 490s, the overall average transfer rate was found to be 1.125 +/- 0.257 MBps, while the average network transfer rate of 3.632 +/- 1.542 MBps was determined. This compares to an average overall transfer rate of 0.389 +/- 0.061 MBps and average network transfer rate under similar conditions of 0.568 +/- 0.060 MBps using Ethernet. For disk-to-memory transfer from a parallel transfer disk (PTD) on a Sun 4/470 to the 2K display frame buffer on a Sun 4/370, the PTD portion of the transfer required 1.2 seconds (6.7 MBps) and the network portion required 1.04 seconds (7.7 MBps) for an overall transfer rate of 3.6 MBps.