The cellular toxicity of extracts on Vero and on MDCK cells was assessed by dye uptake method using neutral red (12) in 96-well tissue culture plates (8 mm diameter, Falcon Plastic, NJ). Only living cells are able to manage the active uptake of neutral red. Confluent monolayers of cells were treated with 100 ml 2-fold serial dilutions of extracts prepared at concentrations of 200, 100, 50 and 25 mg ml À1 in four replicates and incubated at 37 C in a humidified atmosphere of 5% CO 2 for 72 h. The supernatant was removed and 200 ml neutral red solution (0.005%) in optimum was added. The microtiter plate was further incubated for 3 h at 37 C. After removal of the supernatant, the dye incorporated by the viable cells was extracted with 100 ml ethanol/water/glacial acetic acid solution (50 : 50 : 1) by shaking for 15 min. The absorbance was measured on an ELISA reader using Ascent software at 540 nm. The cytotoxic concentration that caused the reduction of viable cells by 50% [CC 50 ] was calculated from dose-response curve.