Total plasminogen activator (PA) activity, tissue-type PA (t-PA) activity, urokinase-like PA activity, and immunoreactive t-PA were measured in benign breast tumors (fibroadenomas), primary breast carcinomas, axillary node metastases, and chest wall recurrences. Total PA activity did not differ significantly in the different types of tumors. However, benign tumors contained predominantly t-PA activity. Urokinase-like PA activity was significantly higher in the malignant tumors compared with the benign group. Both t-PA activity and immunoreactive t-PA were significantly lower in chest wall recurrences compared with primary carcinomas. The ratio of t-PA to urokinase activity was significantly decreased between stages 1 and 3 in the primary tumors. Also, immunoreactive t-PA levels were significantly lower in stages 2 and 3 compared with stage 1. No correlation was found between PA (either total or its different forms) and tumor grade, histological type, or the presence or absence of axillary node metastases.