Emerging nanotechnology applications in the fields of medicine and biology often involve the use of nanoparticles for probing biological processes and structures or for constructing sophisticated nanoscale drug delivery mechanisms. Nanoparticles are already being used with dramatic success in biomedical applications. However, relatively little is known about the potential biological risks from these nanoparticle applications inside the body. The identity of nanoparticles in a biological medium, in terms of their interaction with that medium, is largely determined by the proteins that dress the particles. Since many of the toxic and therapeutic uses of nanoparticles involve the introduction of nanoparticles into the bloodstream of humans and other animals, it is particularly important to know how nanoparticles interact with blood proteins. New research performed in the Polymers Division at the National Institute of Standards and Technology (NIST) directly addresses this issue and explores the effects of nanoparticle size (5nm to 100nm) and a whole range of important blood proteins.