The aim of this review is to briefly describe some colorimetric methods that are commonly used to evaluate a new chemical entity (NCE) on cell cultures in non-clinical oncology discovery research. These methods have the distinct advantage over other techniques in that they can be applied and used in a cell monolayer or a suspension culture. Both protein assay determination and cell viability assays may be conducted using these culture systems. The viability of cell cultures is routinely assessed by utilizing the metabolic capacity of cells which biochemically convert chemicals (usually color dyes) which can then be conveniently measured at specific wavelengths using a multi-well plate reader. Resazurin (Alamar Blue) is an example of one of these metabolically active compounds. Resazurin is a nontoxic dye that can also be used to measure migration and cellular invasion without resorting to sacrifice of the cells during the test procedure. Another is 5-bromo-2-deoxyuridine (bromodeoxyuridine or BrdU) which is a thymidine analog that incorporates into the DNA of dividing cells during the S-phase of the cell cycle. We will also discuss the colorimetric version of the traditional 3H-thymidine incorporation and immunoenzymatic assay used to measure DNA synthesis and its application to discovery research.