In the cytotoxicity panel offered by IONTOX (example data in the figure to the left), Membrane integrity (GST), cell number (propidium iodide), and mitochondrial function (MTT and ATP) are all monitored over a broad range of exposure concentrations. When running these assays, care is taken to ensure that the concentration where efﬁcacy is half maximal (EC50) is included. When the chemical rotenone was tested, the data in the panel of four graphs above tells an interesting story. After a 24 hr exposure, there was no cell death as determined by glutathione S-transferase leakage (GST). There was a reduction in cell number (upper right panel) and a pronounced reduction in both ATP and MTT (lower left panel). Taken together (lower right panel) these data demonstrate that the test molecule (rotenone) has its primary effect on mitochondria, causing a inhibition of complex II (MTT), and a reduction in cellular ATP levels. The loss of cellular energy resulted in a slowing of cell replication. Clearly, vastly different conclusions would have been made if only ATP or only membrane integrity had been monitored.