Imaging of sentinel nodes is a valuable technique in the management of some types of cancer. Several different radiopharmaceuticals have been successfully employed in the technique, but there have been few systematic studies to examine the relationship between physicochemical properties of the radiopharmaceuticals used and in-vivo performance. The present study describes the preparation and characterisation of radiocolloids of similar chemical composition but differing in particle size distribution in an attempt to identify the role of variations in the single parameter of size.