A previous version of this paper was circulated under the title “Revisiting Cooperation in the Prisoners’ Dilemma”.In this paper we obtain the value that experimental subjects attach to a prisoners’ dilemma game by applying a related procedure to BDM (1964). We also obtain the value of a closely related game which does not incorporate any social dilemma. By comparing both values, we are able to classify subjects in different categories: (i) 16% of the subjects responded to the social dilemma by playing the cooperative strategy, (ii) The remaining subjects (84%) did not played the cooperative strategy and moreover, 53% of the subjects behaved as if the social dilemma was not an issue at all.Financial support from centrA: is acknowledged. Pablo Brañas acknowledges the hospitality of IESA-CSIC during this research. Antonio J. Morales acknowledges financial support from MCYT and FEDER grant number BEC 2002-02852.