The present invention relates to biomarkers for preeclampsia as well as treatment of this disease. In particular, the invention relates to methods for diagnosis or aiding in the diagnosis of preeclampsia of a pregnant female mammal to detect elevated levels of free haemoglobin, particularly free fetal haemoglobin. This facilitates and makes possible early diagnosis and clinical intervention when a preeclamptic condition is found. In addition, the invention relates to a method to treat female mammals with preeclampsia with the purpose to reverse the pathological conditions associated with this disease.