Changing medium and passaging cell lines.

Cell lines are widely used in biomedical research. This protocol describes the methods used routinely to change the medium and passage the cells. Medium changes keep the cells healthy by providing fresh nutrients, while cell passage or splitting is required to maintain cells in exponential growth. Despite the simplicity of the methods used, each cell line has idiosyncracies. Whether working with one or several cell lines, there is no substitute for knowledge of their needs, including the range of phenotypes and growth patterns under different physical and nutrient conditions. Given the necessary care and attention, most cell lines are easy to maintain and grow.