Phenotypic changes of integrin and metalloproteinase secretion of the invasive human cytotrophoblast are regulated by cytokines and growth factors, but how this occurs is not completely understood. We used 24-h cytotrophoblast cultures from first trimester pregnancies to investigate the effects of leptin and cytokines on the expression of the alpha2, alpha5, and alpha6 integrin subunits and on the activity of metalloproteinase-2 (gelatinase A) and metalloproteinase-9 (gelatinase B). The alpha2 subunit was marginally upregulated by leptin and interleukin-1alpha (IL-1alpha). All compounds tested upregulated, in some degree, the alpha5 expression. The a6 integrin subunit was massively upregulated, by leptin, interleukins, and transforming growth factor-beta. None of the factors tested affected metalloproteinase-2 activity, but the activity of metalloproteinase-9 was upregulated by leptin and IL-1alpha. In conclusion, leptin and IL-1alpha actively induce some of the changes that cytotrophoblasts undergo to achieve a more invasive phenotype. A novel role for leptin is proposed during early pregnancy: leptin might be an autocrine/paracrine regulator of cytotrophoblast invasiveness during implantation and placentation.