Erythrocin B is an effective, non-toxic and convenient vital exclusion stain for mammalian cells in monolayer culture. This dye is taken up by dead or non-viable cells, but excluded by viable cells. The uptake is based on the fact that those cells whose plasma membranes have been damaged take up the stain and therefore considered as non-viable. Under light microscopy, non-viable cells appear pinkish-red, while the viable cells remain clear. Erythrocin B works on a similar principle as Trypan blue, one advantage being it is less toxic to the cells to be counted. BCL025 is sterile filtered solution of erythrocin B in Dulbecco's phosphate buffered saline. It is typically used at 0.1% concentration for cell culture applications.