Biomonitoring is measurement which indicates conditions in vivo. The aim is to obtain dose-response relationships of internal dose (as near to the target as possible) related to biological changes occurring before clinical signs of poisoning appear. For humans the material available for examination is limited and only accessible samples such as blood, urine or excretions, e.g. exhalation or saliva, can be used. For experimental animals such restrictions do not apply and measurements in individual tissues may be made after death.