Histopathology is almost entirely based on subjec- tive human interpretation of visual images. The dominant role of human interpretation is explained by the complex- ity of the images seen down the microscope and the very efficient processing of this information by the human brain. Evolution has produced Homo sapiens with high resolution vision and a large biological neural network to interpret those data. Pathologists have been trying for some time to combine their human skills in histopatho- logical diagnosis with the advantages offered by comput- er systems. Expert systems are computer programs designed to process knowledge and reach the diagnostic decision in the same way as human experts.1-5 Methods which allow diagnostic knowledge to be represented with in a computer program include rules, artificial neural net- works (ANNs) and inference networks.1 ANNs can com-