Implanted biosensors are now available that permit the continuous telemetric monitoring of physiological and biochemical parameters in experimental animals, and have been proved useful in toxicological studies to minimize not only the artifacts due to animal handling and restraint but also to improve animal welfare. In addition, non-invasive and currently expensive methods such as magnetic resonance imaging (MRI) and nuclear magnetic resonance spectroscopy are available for the visualization of pathological finding and determination of the distribution of a test chemical in laboratory animals, respectively, which further contribute to improved animal welfare.