During the 20th century there were major advances in our understanding of disease, in the discovery and development of new drugs, and in our understanding of how to use drugs for maximum therapeutic benefit. We now have antibiotics and vaccines to prevent and treat infections, good anaesthetics that enable sophisticated and complex surgical procedures to be carried out, and medicines to treat conditions such as asthma, diabetes, heart disease and high blood pressure. We are beginning to understand more about cancer, HIV and mental disorders. In all these medical advances, using whole animals in research has played a vital role in ensuring success. From Domagk's discovery in 1935 [1] of the in vivo anti-bacterial potency of prontosil, which was a precursor of the sulfonamide anti-infective drugs, to the introduction of selective cyclooxygenase 2 inhibitors following in vivo studies that showed the importance of this enzyme in inflammation [2], responses in the whole animal have been crucial in the discovery of new drugs. The discovery and development of antihypertensive drugs illustrates the importance of such in vivo studies.