The tradition of testing the poisonous properties of food and drink by administering the material to animals extends back through the history of mankind. In some civilizations the expediency of employing human beings as professional ‘tasters’ was an acceptable practice. The use of humans for this sort of testing is unacceptable under present-day moral and ethical values. When we adopt the approach that animal testing may predict pharmacological or toxicological responses for man, we do so from a conviction that there is a common-ground plan for all living matter. Indeed, the major biochemical discoveries of the last three decades lend support for this conviction. As we have come to use animals more to predict the response of humans to drugs, we have come to realize that the similarities between animals and man are great, but so are the differences. In a phrase, we have become pharmacologically sophisticated.