Two conventional systems - freshly-isolated hepatocytes and hepatocyte
s in culture - are now widely used for toxicity testing, each possessi
ng advantages and disadvantages, More-recently developed alternative s
trategies, which try to minimise the disadvantages apparent in the con
ventional systems, are described. Results obtained from these alternat
ive strategies are presented, and the importance of culture as a deter
minant of toxic response is emphasised. Evidence is presented that red
uction of the tetrazolium dye, MTT, is a measure of nucleotide redox b
alance in hepatocytes, rather than of mitochondrial performance as pre
viously believed.