Protein assay or protein quantitation is an integral part of any laboratory workflow involving protein extraction, purification labeling or analysis. Cell lysates are assayed to verify success of the lysis step and to normalize multiple samples for storage or side-by-side comparison. Proteins obtained from a purification procedure are assayed to determine yield. Purified proteins that will be labeled with biotin or conjugated to reporter enzymes are typically assayed to ensure that the labeling reaction is prepared with appropriate stoichiometry. Given the wide range of chemicals that may be present in different kinds of samples, it is amazing that there exist protein assay reagents that are capable of reliably and specifically measuring the protein component.