Wnt genes are transforming to mouse breast epithelium and are hormonally regulated in vivo. To assess their role in another endocrine-responsive human cancer, the expression of seven Wnt genes (Wnt 2, 3, 4, 5a, 7a, 7b and 10b) in normal human endometrium and endometrial cells, and endometrial carcinoma tissues and cell lines was investigated by ribonuclease protection analysis. Wnt2, 3, 4 and 5a mRNAs but not Wnt7a, 7b or 10b mRNAs were expressed in primary culture of normal endometrial epithelial (NEE) and stromal (NES) cells. In contrast, in four endometrial carcinoma cell lines (RL95-2, HEC-1-A, AN3 CA and Ishikawa), Wnt2 and Wnt3 mRNAs were absent. Wnt4 was expressed in only one out of four cell lines (RL95-2), and Wnt5a was much lower. Wnt7a and Wnt7b mRNAs were expressed in three out of four cell lines (RL95-2, HEC-1-A and Ishikawa). Wnt10b mRNA was expressed in RL95-2 and AN3 CA. In fresh tissues, all Wnt genes apart from Wnt10b were expressed in normal endometrium and endometrial carcinoma. Similar to the cell lines, the level of Wnt4 mRNA expression was significantly higher in the normal endometrium than endometrial carcinoma. Wnt2, 3 and 5a mRNAs were also lower in endometrial carcinoma compared with normal endometrium. There was no difference in the level of Wnt2, 3, 4 and 5a mRNA expression between proliferative phase and secretory phase of the menstrual cycle, or between either menstrual phase and the first trimester of pregnancy. In vitro, progesterone and/or 17beta-oestradiol had no effect on Wnt2, 3, 4, 5a and 7b mRNA expression in NES and all endometrial carcinoma cell lines. The data indicate that all Wnt genes were expressed in vitro, six out of seven Wnt genes (Wnt 2, 3, 4, 5a, 7a and 7b) were expressed endogenously in the human endometrium, their mRNA expression was hormonally independent and Wnt4 gene down-regulation as well as down-regulation of Wnt 2, 3 and 5a may be associated with endometrial carcinoma.