The Ninth International Symposium of the Esteve Foundation was held in Lloret de Mar (Girona, Spain; 4-7 October 2000). All lectures discussed the Optimal Dose Identification. It was chaired by Alasdair Breckenridge from the Department of Pharmacology & Therapeutics, University of Liverpool, and there were a total number of 29 participants. The proceedings of the symposium were published by Elsevier Sciences.