The second Esteve Foundation Research Prize was awarded to F. Javier Ayesta and Jesús Flórez, from the Department of Physiology and Pharmacology of the Faculty of Medicine of the University of Cantabria, for their study Tolerance to respiratory actions of sufentanil: functional tolerance and route-dependent differential tolerance, published in the Journal of Pharmacology and Experimental Therapeutics in 1989 (250:371-378). The jury was formed by Profs. Gerhard Levy, of the University of Buffalo (United States), Walter Osswald (Portugal) and Sergio Erill (Spain), who considered that this was a fundamental contribution to the knowledge of the mechanisms of narcotic dependence. The elucidation of the exact nature of these mechanisms represented a major step in the design of strategies aimed at overcoming the problem of drug addiction.