The xerographic mammography records of 3,002 patients with breast disease were reviewed and classified according to the criteria of Wolfe. The parenchymal P2 pattern occurred in 59% of patients with cancer and in only 16,9% patients under the age of 40 without cancer, but the incidence of the DY pattern was much the same in patients with cancer and in those without cancer in almost all the age groups studied. The incidence of the P2 pattern tended to rise slightly in patients without cancer, whereas the incidence of the DY pattern tended to remain the same in all groups. The findings of Wolfe and others have been confirmed by this study, which also supports the suggestion that women under the age of 40 undergo a baseline xerographic examination of the breasts for cancer and that subsequent screening be based on the presence of a P2 pattern. This will involve a selection of 16,9% of the under 40-year-old subjects without cancer who might, on screening be expected to show 60% of the cancers in each decade after the age of 40. This information coupled with other factors indicating a high risk for the development of breast cancer, such as florid epithelial dysplasia, a previous history of breast cancer or a family history of breast cancer, should increase the yield of early carcinomas at a preclinical stage and reduce costs of a screening programme.