New medicines require testing because researchers must measure both the beneficial and the harmful effects of a compound on a whole organism. A medicine is initially tested in vitro using tissues and isolated organs, but legally and ethically it must also be tested in a suitable animal model before clinical trials in humans can take place. The animal tests provide data on efficacy and safety. They not only identify potential safety concerns, but also determine the doses which will be given to volunteers and patients during the first human trials. Testing on animals also serves to protect consumers, workers and the environment from the harmful effects of chemicals. All chemicals for commercial or personal use must be tested so that their effect on the people and animals exposed to them is understood. The chemicals that we use day-to-day can accumulate in the water, ground or air around us, and their potential impact on the environment must be researched thoroughly.