A follow-up study of 105 patients with microdochectomy for nipple discharge during the ten year period from 1965 to 1974 revealed that cancer developed in seven of the cases. The histology of the seven cases consisted of atypical hyperplasia in the terminal duct or lobular neoplasia. Accordingly, patients with either of the above histological findings were regarded as high risks for the development of breast cancer. Twenty such high risk patients were selected from 1850 patients biopsied for benign breast disease during the eleven year period from 1975 to 1985. This follow-up study revealed that five of the 13 patients (38%) with atypical hyperplasia in the terminal duct and two of the seven patients (28%) with lobular neoplasia developed breast cancer. Microphotocytometry using TV image analyzed system showed that the mean +/- standard deviation of the nuclear area and the absorbance were, respectively, 46.79 +/- 2.84 and 0.42 +/- 0.01 in fibroadenoma, 62.93 +/- 12.15 and 0.32 +/- 0.02 in precancerous lesion and 86.16 +/- 14.38 and 0.44 +/- 0.07 in breast cancer.