Color enhanced transmission electron micrograph of the liver of a hamster treated for four days with phenobarbital. One of the major functions of the liver is to metabolize exogenous compounds, such as drugs. In this image, we see selective hypertrophy of the smooth endoplasmic reticulum in response to phenobarbitol. This hypertrophy is accompanied by the increased production of drug-metabolizing enzymes in the rough endoplasmic reticulum.