The accurate quantitation of proteins and an analysis of their purity are essential in numerous areas of scientific research, and are a critical factor in many clinical applications. The large and varied number of techniques employed for this purpose is therefore not surprising. The selection of a suitable assay is dependent on factors such as the level of sensitivity required, the presence of interfering agents, and the composition of the protein itself. Here, protocols for the most commonly used protein determination methodologies are outlined, as well as for the more recently adapted technique of quantitative immuno-polymerase chain reaction.