The authors analyse the course of the total haematic hystamine rate in 13 women with breast cancer. They find that neoplasm take a significant increase of the histamine rate in comparison with the controls, while the mastectomy quickly is followed by the normalization of these values. They conclude that, as already suggested for others kinds of neoplasms of the lung and gastroenteric tract, also in the neoplastic pathology of the breast, the haematic hystamine dosage is a useful parameter for the monitoring the course of the illness.