Cytotoxicity testing of anticancer drugs requires techniques which are
sensitive, reproductible and applicable to large scale testing using
automated instruments. End point staining of cells or viability stains
are reliable but they are often not sensitive enough or not suitable
for automation. We have already described a fluorometric cytotoxicity
assay using a non fluorescent substrate, Alarmar Blue, which upon redu
ction in living cells, yields a fluorescent product. This assay is sen
sitive and highly reproductible but it is limited since automated fluo
rescent plate readers are not found frequently in laboratories. The co
nditions are now described for using Alamar Blue as a substrate in a c
olorimetric cytotoxicity assay. This new economical assay could be use
d with advantage for large scale screening of cytotoxic agents in micr
otitration plates.