The events that regulate trophoblast invasion need to be characterized at the transcriptional level. Several types of gene products may be involved in various stages oftrophoblast infiltration, including integrins, matrix metalloproteases (MMPs) and extracellular matrix (ECM) proteins. Autocrine or paracrine regulators of cytotrophoblast proliferation or differentiation in vitro (e.g. growth factors and cytokines, as well as oxygen tension) could be characterized mechanistically at the transcriptional level. Large-scale gene expression profiling of trophoblasts of distinct invasive stages could be carried out on fixed tissue obtained by laser-directed microdissection. This information may shed light on physiological implantation and placentation, as well as on the interpretation of pathological processes such as pre-eclampsia. The applications of DNA microarrays are ideal for studies of genomic structure (e.g. mutation and polymorphism analyses) and monitoring of gene expression. The ultimate goal is to understand the critical events underlying growth, development, homeostasis, 'behaviour and the onset of disease at a genomic level. Microarrays detect gene expression levels in parallel by measuring the hybridization of labelled, single-stranded DNA to many thousands of partial or whole gene sequences immobilized on a glass surface (the 'chip'). Microarrays are available both commercially and can be manufactured in house.