Morphometrical measurements of nuclear area and form factors are carried out by means of a semiautomated image analyzer on 90 cases of ductal breast cancers and on lymph node tumor deposits. The value of the mean nuclear area in lymph node metastases is significantly higher than in primary tumors regardless of the size of the tumor. Since the value of mean nuclear area is also significantly higher in primary tumors with lymph node involvement than in those without lymph node involvement it is possible to assume that primary tumors with large-nucleus areas are more liable to invade lymph nodes. No significant differences are noted as far as the form factors are concerned.