The United States Food and Drug Administration (FDA) requires nonclinical studies of new drugs, food additives and chemicals to predict their safety and potential efficacy in humans. The significance of the information gained from these studies requires that they be conducted according to sound scientific principles and with strict attention to quality assurance and quality control. Human health and safety are dependent upon the decisions made from these studies. The discovery of the lack of companies' adherence to these principles led to the development of the good laboratory practice (GLP) regulations, the driving force behind the quality of nonclinical laboratory studies. As the 25th anniversary of the publication of the regulations approaches, a description of the events leading to the proposal of the GLP regulations provides understanding about their significance and the importance of their use in assuring the quality and integrity of nonclinical safety data. Copyright © 2003 John Wiley & Sons, Ltd.