For almost forty years insoluble barium sulfate has been the standard opaque medium used in alimentary tract examinations. During this period many attempts have been made to increase the time during which the barium will stay in suspension. The large number of proprietary products available indicates that the perfect suspens on is yet to be made. Proprietary Preparations A large portion of the annual output of highly purified BaSO4 is processed by adding suspending and flavoring agents—occasionally by grinding, milling, or passing the barium through a colloid mill—and packaging. Few of these proprietary mixtures carry labels that are truly informative. As so ably expressed by Hodges, these “labels appear to have been composed by sales managers rather than chemists or pharmacists and seem calculated to mislead rather than inform” (11). Indeed, the labeling laws of the United States Pure Food and Drug Act do not require that these media be precisely or completely labeled except for the manner in which they ...