The retrospective analysis of 672 consecutive patients with breast cancer revealed malignant pleural effusion and lymphangitic carcinomatosis of the lung to be the sites of first relapse of the disease in only 2% and 1%, respectively. In half of the 10 patients with malignant pleural effusions evaluable for survival, generalization of the disease was recorded at 51 months (range 0-197 months); the corresponding data for patients with lymphangitic carcinomatosis of the lung (n = 7) were 19 months (range 9-44 months). This difference was statistically significant (p < 0.05). The median survival of patients with pleural effusions and with lymphangitic carcinomatosis of the lung was 22 and 8 months, respectively (n.s.).