New Internet technologies offer excellent chances to build high-quality on-line learning media for the education in medicine. Especially, the teaching of diagnostics with medical imaging as well as medical image processing can be supported by the excellent visualization and interaction capabilities. In cooperation with three radiological departments at German universities in Munich, Erlangen and Würzburg, the case-based open distributed Internet text book (ODITEB) for tumor diagnosis of the GI-tract, liver, pancreas and thorax has been developed at the Institut für Medizinische Statistik und Epidemiologie (IMSE) of the Technische Universität München. It offers a big collection of clinical tumor cases located on servers at the provider sites Munich, Erlangen and Würzburg, visualization and interaction similar to a real CT or MRI console, original DICOM data, X-rays and endoscopic and endosonographic videos, and expert-guided tours through the cases. In a first evaluation in summer 1998, 32 medical students graded the application with 1.9 ('good') on a scale from 1 ('very good') to 5 ('very bad'). The textbook supports German language, an English version is in preparation. In a second part, it contains lessons in medical image processing for students of medical informatics. An ODITEB release 2 with several improvements will be finished until February 2000. The use of the textbook is free of cost.