Leukocytes are activated in women with preeclampsia, but the class of leukocyte most likely to cause vascular dysfunction is not known. We hypothesized that neutrophils may be the class of leukocyte most involved in causing this dysfunction because neutrophils are the most abundant of the leukocytes and their numbers increase during pregnancy. In this study we compared vascular infiltration of neutrophils (CD66b) with monocytes/macrophages (CD14) and lymphocytes (CD99) in normal non-pregnant women (NNP), normal pregnant women (NP), and preeclamptic women (PE). There was no significant difference in the infiltration of lymphocytes into the maternal vasculature in PE as compared to NNP or NP. There was significantly more neutrophil infiltration into the systemic vasculature in PE women than in NP and NNP women. Monocytes/macrophages were present in tissue but not in vessels. We speculate that neutrophils are the class of leukocyte that causes the majority of vascular cell dysfunction in preeclampsia.