Wnt gene expression was investigated by ribonuclease protection analysis in human breast cancer, nontumorous breast tissue, and a variety of human breast cell lines. We report the expression of Wnt3, Wnt4, and Wnt7b in human breast cell lines and Wnt2, Wnt3, Wnt4, and Wnt7b in human breast tissues. Wnt3a and Wnt7a were absent in the cell lines and tissues tested. The level of expression of Wnt2 and Wnt4 was 10- to 20-fold higher in fibroadenomas than it was in normal or malignant breast tissue, and in 10% of tumors Wnt7b expression was 30-fold higher than in normal or benign breast tissues. In contrast to the mouse, in which Wnt1 and Wnt3 are involved in tumorigenesis, our results suggest that Wnt2, Wnt4, and Wnt7b may be associated with abnormal proliferation in human breast tissue.