Estimation of cell number by neutral red content. Applications for proliferative and survival assays.

A simple photometric method for estimating viable cell number in culture is described. When cultured cells are allowed to internalize 0.005-0.01% neutral red for 1 h, the amount of accumulated dye is directly proportional to cell number. The linear relationship holds for adherent and suspended cell lines. Thus, dye content reflects cell number. Since dye content is easily measured by instruments that photometrically scan microtiter trays, proliferative and survival (cytotoxic) responses can be easily quantitated.