There is an increasing need for teleradiology services that enable images to be sent to other centres for further opinion, plus the collation of research data with images from many different medical institutions. Mammography has specific and demanding requirements, and in testing a new Dicom compression and encryption tool it was apparent that it can cope with very large files such as a set of four Dicom mammograms. The 256 bit (32 characters) encryption provides appropriate data protection for transmission of the compressed images, while the original Dicom images remain unchanged on the host system. Four sets of Dicom mammograms were compressed and prepared on disc as a series using the originals in one set, and varying levels of compression to six other series. These were viewed by various consultants on a personal computer to determine whether the image quality is acceptable for diagnosis, and evaluated on a scale of 1–5. A 34 MB patient set can be compressed to fewer than 300 kB without losing data. A separate analysis of all pixels in the image for both original and compressed formats give an indication of 'Lossless' and 'Lossy' 1/3 levels. The applications of this technology will be considered.