Angiotensinogen, a protein present in blood, plays a critical role in the regulation of blood pressure. Angiotensinogen is cleaved by renin, an aspartic protease, to release angiotensin-I, the peptide precursor to several vasoactive compounds that are critical for the regulation of blood pressure. Recent studies have shown that, in a type of redox switch, the two forms of angiotensinogen—reduced and oxidised—bind differentially to renin¹, a difference which may play an important role physiologically, particularly in disease states such as pre-eclampsia where the balance between the oxidised and reduced forms is upset. Can these two forms of angiotensinogen be discriminated and quantified, and thus exploited in order to probe conditions such as pre-eclampsia further? The two forms of this critical blood protein are being investigated using surface plasmon resonance and analytical ultracentrifugation in order to examine differences between the two redox forms, in terms of binding to renin and various antibodies.