Objective: The purpose of this study was to investigate whether the altered vascular resistance in pregnancy and preeclampsia results from alterations in intrinsic vascular smooth muscle properties or from external influences on vascular smooth muscle function. Study Design: We studied subcutaneous resistance arteries from women with preeclampsia, from normal pregnant women, and from nonpregnant women, that were obtained during cesarean delivery or gynecologic surgical procedures, in a pressure myograph. Arteries were denervated, and smooth muscle cells were loaded with calcium indicator fura-2. Contractile properties were tested in physiologic saline solution and during potassium- and norepinephrine-induced constriction at various pressures. In addition, endothelial function was assessed. Intracellular calcium and tone were measured continuously. Results: No significant differences in basal tone, constrictor, and myogenic responses were found between groups. Contractile element calcium sensitivity was significantly increased in women with preeclampsia. Norepinephrine caused an increase in calcium sensitivity in all groups. Conclusion: Vascular smooth muscle calcium sensitivity is increased in preeclampsia. (Am J Obstet Gynecol 2002;186:148-54.)