Endometrial cancer is the fourth most common female malignancy in women in developed countries. Estrogen, and to a lesser degree, progesterone, regulate specific target genes that are involved in endometrial tumorigenesis. A family of proteases involved in cellular proliferation, extracellular matrix degradation and thus, implicated in tumorigenesis, and regulated by estrogen and progesterone in a number of systems, are the tissue kallikreins (KLKs). KLK4, a new member of the KLK gene family, was found to be expressed to varying levels in a number of endometrial cancer cell lines- HEC1A, HEC1B, Ishikawa, RL95-2 and KLE- at both the mRNA and protein level. On the addition of 10 nmol/L estradiol, progesterone, or a combination of both over a 48 h period, an increase in the intracellular protein levels of K4 were observed when compared to the control (untreated) cells. We have also identified a novel KLK4 transcript with a complete exon 4 deletion. The significance of this alternative transcript, which would give rise to a truncated protein without a serine residue (which is essential for catalytic activity), is yet to be established. These cell lines now provide a model system to study the role of KLK4 and the molecular mechanisms of KLK4 regulation by estrogen and progesterone, in endometrial tumorigenesis.