A so-called bottom-up approach of a Picture Archiving and Communication System (PACS) is initiated by existing clinical questions. It is investigated how far existing Data-Acquisition (DA) modalities combined with the existing computer infrastructure of the hospital can provide soil to a, at first local, PACS system. Examples of current research projects in Digital Subtraction Angiography (DSA), Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) demonstrate how image and raw data processing evolve from applications based on a general matrix manipulation software package to projects within the field of PACS. Starting from the existing facilities a stepwise increase of connections and expansions of required features is going to be brought about by separately considering the picture system, the communication system and the archive system. A three step phasing is proposed: (1) Software linking; (2) Hardware linking: small scale; and (3) Hardware linking: local area network. Examples are given from the first phase, i.e. the development and expansion of software on existing DA-modalities or processing hardware to receive the data on floppy disk, hard disk or tape. Data are converted and transported for further processing: (a) within the department; (b) between hospital departments; and (c) between research centres. With regard to the picture system special attention has to be given to the requirements for digitizing analogue film images and the reading of images from monitor screens instead of films on lightboxes.