2. You may need to add dilution of drugs or other agents at this time or after cells have attached overnight.

3. Incubate cells for the desired time at 37 °C.

4. To fix cells, add 50 ml of cold 50% TCA (adherent cells) or 80% TCA (suspension cells) to each well dropwise.

5. Fix at 4 °C for 1-3 hours.

6. Remove the liquid by inverting the plate.

7. Rinse the plates 5 times with water, tapping on paper towels after rinsing.

8. Air dry the plates (face up) in room temperature for 12-24 hours.

9. Add 100 µl 0.4% sulforhodamine B (SRB)/1% glacial cetic acid to each well.

10. Incubate at room temperature for at least 5 minutes.

11. Rinse the plates 3 times with 1% glacial acetic acid, tapping on paper towels after rinsing.

12. Air dry the plates (face up) in room temperature for 12-24 hours.

13. Add 100 µl of 10 mM Tris and shake until all bound SRB is into the solution.

14. Read on a microplate reader at 515 nm.