This study was addressed to evaluate the temporospatial pattern of key components of the kallikreinkinin system in human uterus in luteal phase (n = 7), early pregnancy (isolated spontaneous abortions, n = 11; ectopic pregnancies, n = 9), idiopathic preterm deliveries (n = 5), and term gestations (n = 12). Tissue kallikrein mRNA and protein and the type 2 bradykinin receptor (B2R) protein were expressed in luminal and glandular epithelium and in endothelial cells of stromal and myometrial blood vessels, while tissue kallikrein mRNA and B2R, but not tissue kallikrein protein, were observed in decidual cells and in arteriolar and myometrial muscle. A greater signal intensity for tissue kallikrein mRNA and protein and of B2R protein was observed in the early pregnancy samples. The sites and variations of the tissue kallikrein mRNA and protein and of the B2R protein in the human uterus and in fallopian tubes during the luteal phase and in pregnancy coincide with those described for other vasoactive effectors such as nitric oxide, prostacyclins, growth factors, and renin. The uterine localization of the main enzyme and receptor of the tissue kallikrein-kinin system in key sites for embryo attachment, implantation, placentation, maintenance of placental blood flow, and parturition supports the notion that the kallikreinkinin system participates in these processes, probably through vasodilation, increased vasopermeability, enhanced matrix degradation, stimulation of cell proliferation, and myometrial contractility.