The spatiotemporal distribution of two angiogenic growth factors, platelet-derived endothelial cell growth factor (PDECGF) and vascular endothelial growth factor (VEGF) were determined using immunohistochemistry on sections of human placentae from each trimester of pregnancy. In the first trimester PDECGF was detected in trophoblast and in a band in the centre of the villous core. During gestation staining spread throughout the stroma but began to weaken in trophoblast until, by term, it was found only in stroma and in some endothelial cells. VEGF was detected exclusively in cytotrophoblast during the first trimester and then in syncytiotrophoblast throughout the remainder of pregnancy. Western blot analysis revealed that PDECGF antisera bound to three bands approximately 27, 47 and 94 kDa. The lowest band was not detected in platelet lysate and may represent an alternatively processed form of this peptide in placenta. VEGF antisera bound strongly to bands approximately 36, 46, 54, 56 and 64 kDa. The intensity of most bands increased between the first and second trimesters, consistent with an increased level of angiogenesis as the placenta develops. The presence of both factors in trophoblast in early pregnancy may be indicative of the trophoblast playing an active role in influencing the development of the villous vascular network.