Human serum albumin (HSA) protein molecules (blue) with various ligands (red) attached to them, illustration. HSA proteins are the most abundant proteins in human blood plasma. They transport hormones, fatty acids and many drugs through the blood. HSA proteins also play a role in regulating plasma volume. From upper left to lower right the ligands are: azaprazone (anti-inflammatory drug), camptothecin (chemotherapeutic agent), propofol (anaesthetic), halothane (anaesthetic), octadecanoic acid (fatty acid), prostaglandin (fatty acid), bilirubin (waste product from red blood cell breakdown) and ibuprofen (anti-inflammatory drug). For a labelled version of this image, see F037/5974.