Briefly, SRB assay might overestimate the surviving fraction of cells becauseof the presence of cells that were killed by a drug, but not lysed,while results obtained by MTT assay may be influenced by (a) chemical reduction of the tetrazolium by the test agents, which gives rise to spurious levels of formazan; (b) chemical interference with cellular reduction of the tetrazolium; and (c) a variety of metabolic conditions (e.g., depletion of glucose and variations in
pH), which might alter production of formazan from tetrazolium