Electron microscopic study of the breast tumors were carried out on 67 patients. There were 7 intraductal carcinomas and 60 infiltrating ductal carcinomas of the breast. Observations were made on the morphological characteristics of neoplastic cells, myoepithelial cells and basal lamina. Cells organelles in the neoplastic cells are similar in both types of ductal carcinomas. Nuclei are predominantly large and irregular with poor dense chromatin. Often a lot of filaments are around the nuclei. Myoepithelial cells in the infiltrating ductal carcinomas are ultrastructurally the same as seen in the intraductal carcinomas, but they seems to be less numerously than in the intraductal carcinomas. In the intraductal carcinomas of the breast basal lamina is irregular and from time to time is disrupt. In the infiltrating ductal carcinomas basal lamina is usually absent, but sometimes we can find its short fragments.