The cells were then treated with various concentrations (10, 25, 50 and 100μg/ml) of ethanol and chloroform extract of Kappaphycus alvarezii and control DMSO (100µl of 1 % DMSO). The, the cells were then incubated for 24 h and 10 μl of MTT stock solution [5 mg/ml in phosphate buffer saline (PBS)] was added per well and incubated at 37° C for 4 hours in 5% CO2 atmosphere. Then, the medium was removed and washed with PBS; 200 μL of DMSO was added to each well. The intensity of the coloured product was measured using an ELISA microplate reader at 540 nm. The results were expressed as the percent optical density of treated cells to that of the control cells.