BACKGROUND: The objectives were 1. to evaluate if the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine was altered in mild and severe forms of preeclampsia, and 2. to assess the relationship between dimethylarginines and the cytokine response in preeclampsia. METHODS: Asymmetric and symmetric dimethylarginine were measured with high performance liquid chromatography in women with mild (n=13) and severe (n=32) preeclampsia and in normotensive pregnant controls (n=20). Interleukin-4, -6, -8, -10 and tumor necrosis factor-alpha were analyzed by immunoassays in women with mild (n=8) and severe (n=17) preeclampsia and in normotensive pregnant controls (n=14). The Mann Whitney U-test and Spearman Rank test were used for statistical analysis. RESULTS: The plasma levels of dimethylarginine were increased in preeclamptic subjects. The elevation of symmetric dimethylarginine was more pronounced than that of asymmetric dimethylarginine. The control levels of interleukin-6, -8 and -10 were significantly higher at term than at gestational week 32-36. Interleukin-6 and -8 were significantly elevated in subjects with severe, but not mild, preeclampsia, whereas TNF-alpha and IL-10 were not significantly altered. Symmetric dimethylarginine levels correlated significantly with arterial blood pressure and serum levels of creatinine and uric acid. Dimethylarginine levels in plasma were, however, not related to the cytokine response. CONCLUSIONS: Plasma concentrations of both asymmetric and symmetric dimethylarginine were significantly elevated both in mild and severe preeclampsia. Symmetric, but not asymmetric, dimethylarginine correlated to the severity of the condition. Plasma levels of interleukin-6 and -8 were also elevated in severe preeclampsia but no direct correlations were found between these cytokines and dimethylarginines.