The molecular mechanisms regulating uterine relaxation and contraction during pregnancy are poorly understood. In the present study, we used for the first time a functional genomics approach applying gene array technology to identify novel candidate genes involved in the regulation of uterine quiescence and contractility during pregnancy. The purpose of this approach was to obtain a molecular snapshot of the expression profile of gene transcripts as a function of the time dependent process regulating myometrial quiescence. Using this approach, we found several genes whose expression in human myometrium was altered with the onset of labour. For example, the expression of insulin-like growth factor (IGF)-II, calgranulin A and B, and G-protein coupled receptor were decreased while the expression of IGF-binding proteins, Ca(2+)/CaM binding protein kinase C substrate, and angiotensin converting enzyme were increased in the labouring, compared with non-labouring, pregnant myometrium. The differentially-expressed genes include several genes whose roles in myometrial quiescence are yet to be understood, although they have been reported to regulate vascular smooth muscle tone. Our findings illustrate the advantage of a functional genomics approach over a single gene analysis in identifying a large number of novel and potentially important genes mediating uterine smooth muscle contractile activity.