The effect of aqueous extract of Alpinia galangal on AGS and L929 cells proliferation was determined. All five Alpinia galangal extracts, at the concentration of 0-1000 µg/mL, dissolved in dimethyl sulfoxide (DMSO) (Sigma-Aldrich), were added to the wells, 24h after seeding of 5 ×103 cells per well of 96-well plate. DMSO was used as a solvent control. After 24 and 48h of incubation, 20μL of 5mg/mL MTT (Sigma Chemical Company) solution was added to each well, and the plates were wrapped with aluminum foil and incubated for 4h at 37°C. The purple formazan product was dissolved by addition of 100μL of 100% DMSO to each well. The absorbance was monitored at 570nm (measurement) and 630nm (reference) using a 96-well plate reader (Bio-Rad, Hercules, Calif, USA). Data were collected for each four replicates and used to calculate the means and the standard deviations. Optical density of AGS and L929 cells incubated in the presence and absence of the different concentrations of Alpinia galangal was compared together and the percentage of surviving cells was determined using the following formula: