1. Grow cells (50 ml) and experiment in 96-well plates.

2. XTT-tetrazolium is metabolized by the mitochondrial enzymes of live cells to a soluble formazan product.

3. Prepare fresh XTT stock solution (1 mg/ml in PBS).

4. Dilute 1:100 PMS stock (phenazine methosulfate 15 mg/ml in PBS, store in dark and -20 °C.) in PBS.

5. Add 40 ml diluted PMS per ml of XTT solution.

6. Add 50 ml XTT/PMS mix to each well containing cells.

7. Incubate cells at 37 °C for 4 hours.

8. Seal the plates with adhesive plate sealer.

9. Mix by inverting the plate several times.

10. Read using a plate reader at the wavelength of 450 nm.