Abstract: A method of diagnosis of solid epithelial tumours or other abnormalities such as rectal colitis, which comprises size-separating stroma from epithelial cells, separating the epithelial cells from most of the other tissue still present, by reacting the tissue with a monoclonal antibody specific for epithelial cells, collecting the reacted cells bound to the antibody and releasing them from the antibody, whereby the sample contains at least 90 percent epithelial cells by volume of the total tissue of the sample and comparing at least one phenotypic or genotypic characteristic of the sample with corresponding normal epilthelial cells