ABSTRACT
Chemically induced toxicity at the level of the organism has been a subject of study over many years. Initially, changes in the overall physiology of the organism, lethal dose determination, body and organ weight, and gross pathology at the macroscopic level were studied. These parameters are still worth-while and part of routine toxicological examinations. The development of histological techniques made microscopic examination of tissues and determination of toxic effects possible at
a more cellular level. After this, molecular techniques, including Southern, Northern, and Western blotting, became available for sensitive and early identi cation of speci c molecular end points. Changes in the levels of particular proteins or metabolites in tissue, blood, or urine or in in vitro systems that correlate well with certain types of toxicity are now routinely assessed.1
