We compared the potential of five commonly employed cytotoxicity assays (WST-1, XTT, MTT, Brilliant blue and Neutral red assay) to detect anti-proliferative effects of three selenium compounds, sodium selenite, seleno-L-methionine (SeMet) and Se-(Methyl)selenocysteine (SeMCys) on three colorectal cancer cell lines in vitro. Cells were exposed to the selected selenium compounds in the concentration range of 0