A maximum tolerance level of lead in human bloodstream can be considered as an example of biological standard. The advantage of a biological standard's application as a controlling tool is a fact that it determines a comprehensive influence of all sources on the researched object, i.e. an object being under the protection. Its disadvantage is a fact that it allows to detect an excess of a maximum tolerance level only when a pollutant has already penetrated into organism and, possibly, in excessive amounts.