It has long been recognized that detecting cancers in their early, non-invasive stage is the best strategy to control malignant diseases. This has been best demonstrated by the example of cancer of the uterine cervix. Before screening for early signs of this malignancy, the prevalence of invasive cancer of the uterine cervix in the developed world was as high as 30 women per 100,000 and the mortality was 12-15 per 100,000 women per year, (all figures represent age standardized data). Since the introduction of cervical screening programs by Pap smears, the incidence of invasive cervical cancer and mortality due to this cancer has fallen dramatically. In British Columbia, for example, where population screening was introduced 50 years ago, the incidence and mortality have decreased several-fold and are at present below 6 and 3 per 100,000, respectively (1,2). It is believed that these figures could be even lower by encouraging more women into the program and by improving both sensitivity and specificity of the cytology.