The eighth international symposium organized by the Esteve Foundation, Variability in human drug response, was held on October 7-10, 1998 in Sitges. Aspects related to the variability in drug response were discussed. As shown in this symposium, the fact that each patient is different when given one same treatment entails both an obstacle and a challenge for clinical pharmacology. Geoffrey T. Tucker, from the Department of Molecular Pharmacology and Pharmacogenetics of the University of Sheffield, presented this interdisciplinary symposium and supervised its further edition in volume number 8 of the Esteve Foundation Symposia series, published by Elsevier Science.