In a prospective study we measured laboratory variables of hemolysis in 25 patients with HELLP-syndrome. Reduced haptoglobin levels were observed in all 25 patients at diagnosis. Elevated bilirubin and plasma hemoglobin levels were observed in 5/25 patients while an abnormal peripheral blood smear was found in 11/25 patients. Our results suggest that haptoglobin is a sensitive parameter for early detection of moderate hemolysis in HELLP-syndrome and should be included in laboratory screening to aid diagnosis.