This paper presents preliminary results from a pilot experiment dealing with the economic motivations to contribute to Free/Open Source Software (FOSS). Bessen and Maskin [1] argue that in a dynamic sequential innovation framework the standard argument for granting patent protection is no more valid and the innovator has at certain conditions an incentive to fully disclose the results of his works; in these same conditions, a copyright strategy could result in a tragedy of the anticommons [5,2]. We study in the lab the choice of copyrighting or copylefting subsequent innovations in a dynamic setting à la Bessen and Maskin, introducing an innovative experimental design requiring real effort on the part of subjects. The players are asked to actually 'innovate' producing words from given letters, and face the choice to copyright or copyleft their words. Preliminary results show that copyleft is more likely to emerge when royalty fees are relatively high, and when the extendability, modularity and manipulability of inventions is enhanced.