High-content analysis (HCA) of in vitro biochemical and morphological effects of classic (small molecule) drugs and chemicals is concordant with potential for human toxicity. For hepatotoxicity, concordance is greater for cytotoxic effects assessed by HCA than for conventional cytotoxicity tests and for regulatory animal toxicity studies. Additionally, HCA identifies chronic toxicity potential, and drugs producing idiosyncratic adverse reactions and/or toxic metabolites are also identified by HCA. Mechanistic information on the subcellular basis for the toxicity is frequently identified, including various mitochondrial effects, oxidative stress, calcium dyshomeostasis, phospholipidosis, apoptosis and antiproliferative effects, and a fingerprinting of the sequence and pattern of subcellular events. As these effects are frequently non-specific and affect many cell types, some toxicities may be detected and monitored by HCA of peripheral blood cells, such as for anticancer and anti-infective drugs. Critical methodological and interpretive features are identified that are critical to the effectiveness of the HCA cytotoxicity assessment, including the need for multiple days of exposure of cells to drug, use of a human hepatocyte cell line with metabolic competence, assessment of multiple pre-lethal effects in individual live cells, consideration of hormesis, the need for interpretation of relevance of cytotoxicity concentration compared to efficacy concentration and quality management. Limitations of the HCA include assessment of drugs that act on receptors, transporters or processes not found in hepatocytes. HCA may be used in a) screening lead candidates for potential human toxicity in drug discovery alongside of in vitro assessment of efficacy and pharmacokinetics, b) elucidating mechanisms of toxicity and c) monitoring in vivo toxicity of drugs with known toxicity of known mechanism.Classic (small molecule) drug toxicity is one of the major challenges for the pharmaceutical industry, not only because of the associated loss of human life or health, but because of enormous financial loss of past investment and of future revenue potential. Attrition of drugs is progressively more costly the later it occurs. It costs almost two billion dollars to bring the average drug through discovery and development to registration [1]. Furthermore, typically 10-12 years of investment of time by hundreds of pharmaceutical staff will have been mis-spent.Drug safety has been an important cause of this attrition. Analysis of safety attrition of approved drugs over a 25-year period ending in 1999 indicated an annual average of 0.7 approved drugs was withdrawn and two drugs received black box warnings [2]. From 1994 to 2006, the average safety attrition was even higher with 2.1 drugs per year, with 38 drugs withdrawn from the market by the US Food and Drug Agency More than 80% of market withdrawals due to drug toxicity were due to cardiotoxicity and hepatotoxicity. In 2003, druginduced liver injury was found to be the most fr...