We have already reported that stromal fibroblasts of breast cancer tissue (CaF) promoted the growth of breast cancer cells in vitro. It was found that CaF and fibroblasts in normal breast tissue (NF) showed the different growth and contracting activity. Materials were obtained from cancer tissue and normal breast tissue. Cells were prepared by collagenase digestion. The CaF's growth was more rapid than NF's. After a reconstitution of type I collagen, monolayer cultures of CaF and NF were done on collagen gel for 24 hours, then collagen gel was detached from the dish and was being float. After 2 days incubation, an area of collagen gel was measured. A contraction of CaF's gel was greater than that of NF. This showed that CaF had more contracting activity than NF. These results might be indicated that the function of CaF was to contribute the invasive growth of breast cancer cell as well as to secrete the growth factors. Therefore, it is considered, a control of the fibroblasts derived from cancer stroma may play an important role in the treatment of breast cancer.