STUDY 3 This study will assess the effect of acetylcysteine on renal function in healthy volunteers receiving a single IV 100ml dose of Visipaque 320 (iodixanol, equivalent to 320 mg iodine/ml), an iso−osmolar non−ionic radio−contrast agent, via a peripheral cannula. We chose this dose because 100 mls are routinely used in the Royal Infirmary for coronary angiography in CKD patients (Radiology Dept, personal communication). Larger doses of up to 400 ml are then used if an angioplasty is subsequently required. Such doses fall within the doses recommended in the summary of product characteristics, Martindale, and the literature. The safety profile of such doses in healthy adults is excellent; in patients with CKD, iodixanol is at least as safe as other contrast agents.