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determining optimal cell count for MTT - (Sep/21/2011 )


I'm new to the MTT assay and from what I've read, I have to first determine the optimal cell count before performing the assay with my test sample. None of the protocols that I've read for this , ask you to add any cytotoxic compound before adding the MTT. How then will the formazan crystals be formed if I'm going to plate cells with >90% viability? Or am I missing out on something?



With the MTT assay, the viable cells convert the substrate into formazan crystals. Therefore, the toxic agent is not needed for establishing optial cell nubmer. You want to make sure you are within the linear range with your cells and timepoints. Please feel free to look over the manual for the Promega version for more information:

Also, please do not hesitate to contact Promega Technical Services with any questions you may have.

Kind Regards,


O right! I'm sorry my bad.. i didn't quite read the principle properly and therefore misunderstood how the assay works.. Thanks Kevin