The aim of the present study was to evaluate the depth of endovascular trophoblast invasion and associated remodelling of spiral arteries in a transgenic model of pre-eclampsia in the rat, a species showing a comparable deep invasion during normal pregnancy as the human. Pre-eclamptic (PE) transgenic rats (TGR) (hAngiotensinogen female x hRenin male) and non-PE reversely mated (RM) TGR rats were compared to normal Sprague-Dawley rats (C). Day 18 implantation sites were collected and the presence of endovascular trophoblast, fibrinoid, endothelial and smooth muscle cells were evaluated in spiral arteries in three parallel layers in the mesometrial triangle using an image analysis system (KS-400). In a separate group of animals peak-systolic and end-diastolic velocities were measured by Doppler in uterine and arcuate arteries, and the resistance indices (RI) were calculated. In PE and RM rats, the entire mesometrial triangle contained significantly more endovascular trophoblast and vascular fibrinoid deposits than the C group. No difference was found between the groups in the overall amount of smooth muscle surrounding the lumen, but in the PE and RM groups significantly more muscle was present in parts of the contours covered by trophoblast. There was significantly less CD31-positive endothelium in the total lumen contours of the PE and RM groups than in the C group, but in parts of the contours covered by trophoblast more residual endothelium was present in both TGR groups. Comparison of the three layers indicated deeper invasion in both the PE and RM groups than in the C group. By Doppler analysis of the proximal uterine artery the RI was found to be significantly lower in the PE and the RM group than in the C group. In the arcuate artery, the RI was significantly lower in the PE group as compared to the RM and C groups. We conclude that in this transgenic PE rat model there is deeper endovascular invasion of spiral arteries and decreased RI of uterine arteries at day 18 of pregnancy.