At Hamamatsu University Hospital, an ATM + FDDI network was installed in January 1995, when the hospital information system was upgraded. With its unique 'wheel' shape configuration, FDDI automatically backs up in case of an ATM switch failure. The authors implemented a DICOM image database server and DICOM viewer in the Hamamatsu University Hospital ATM + FDDI network. The DICOM standard worked well between different vendor products. In sending 512 x 512, 2 byte CT images, 40% of the transfer time was spent for the network data transfer, which is 70% of the theoretical value of 10 Mb peripheral transfer rate. Meanwhile, ATM load factor increased less than 0.5%. As we have a very fast data transfer network, we must check display speed, hard disc access time, PC bus speed, and display software, in order to enjoy the high speed network transfer fully. The sequence of image transmission within a study is not stated in the DICOM document and is depending on the server. Therefore, there should be an agreement between server and clients, still more than DICOM, in order to make better PACS.