Due to the importance of arginase enzyme in different malignant disorders, the purpose of the present study was to determine and compare the arginase activity in cancerous cells and their normal and benign counterparts. The tissue arginase activity level was evaluated in 30 females with breast cancer, in 6 females with benign breast disease and in 9 healthy control subjects. The arginase activity levels were significantly increased in malignant breast tissues in comparison to healthy ones, while the difference did not reach the level of significance