The anti-Human immunodeficieny virus (HIV) assay was developed in 1987 and was operated for approximately ten years. It is a relatively simple method to determine the ability of a drug to protect cells against the cytopathic effects of HIV. T-lymphocyte-derived CEM cells are added to 96-well microtiter plates along with cell-free HIV and the test agent at 1/2-log dilutions over a multi-dose range. Six days after infection, a tetrazolium reagent, XTT, is added to the wells. In the presence of viable cells, XTT is metabolized to an orange colored formazan, such that the quantity of viable cells, and thus, the protective ability of the test agent, is proportional to the depth of the color. Uninfected cells are also treated with drug in order to determine the cytotoxicity of the drug, if any, to the CEM cells. Screening data and chemical structures for more than 40,000 compounds is available.