A model of the elastic behavior of a biomembrane in response to intercalation of amphiphiles into the bilayer is developed. This model takes into account the bilayer couple hypothesis (Sheetz and Singer 1974), and assumes that incorporation of amphiphiles into one layer of the membrane exerts mechanical work on the elastic biomembrane. The model accounts for an apparent experimental discordance noted by several authors: the variation in area observed upon incorporating amphiphiles is smaller by a factor of about 2 than the variation expected using previous models.