The medical benefits of a drug are not only dependent on its biological effect, but also on its "life cycle" within the organism, from its absorption into the blood, distribution to tissue until its eventual breakdown or excretion by the liver and kidneys.Here, the authors, all of them employed at Pfizer in the discovery and development of new active substances, discuss the significant parameters and processes important for the absorption, distribution and retention of drug compounds in the body, plus the potential problems created by their transformation into toxic byproducts. The authors cover everything from the fundamental principles right up to the latest developments using high throughput methods to analyze the pharmacokinetic properties of active substances.Particular emphasis is placed on the impact of pharmacokinetic parameters on the discovery of new drugs, one of the most challenging tasks in global pharmaceutical research.