Plasma levels of polyunsaturated fatty acids in the n-3 and n-6 classes, which include linoleic, linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids, were quantified with high-performance liquid chromatography in nonpregnant volunteers and in patients with normal pregnancies or preeclampsia at term. The total polyunsaturated fatty acid levels were not significantly different between nonpregnant and normal pregnant patients but was significantly lower in the preeclamptic patients compared with normal pregnant patients. This decreased level could represent altered fatty acid metabolism or altered storage and mobilization from lipid pools. Compared with nonpregnant patients, normal pregnant patients had significantly higher levels of eicosapentaenoic and docosahexaenoic acid. This may reflect normal physiologic changes in pregnancy, and the decreased level of eicosapentaenoic acid seen in preeclamptic patients may play a significant role in the pathophysiology of preeclampsia.