An increasing number of developing countries are considering their highly qualified citizens living abroad as a potential asset for national development. Renewed policies are consequently designed in order to ensure the return of this expatriated talented group. Besides the repatriation-return-option generally enacted in these policies with varying success, a second one has recently emerged : the diaspora option. It consists of the remote mobilisation of intellectuals abroad and their connection to scientific, technological and cultural programmes at home. At the beginning of the 1990s, Colombia began to systematically and consistently apply this option, through the creation of the "Colombian Caldas Network of Scientists and Engineers Abroad". The experience of this strategy has been studied during the last four years by a Franco-Colombian research team. The paper discusses the results of this study. It first contextualises the diaspora option and the Colombian experience by putting it in historical perspective along with the other policies designed to tackle the issue of professionals' migration. It then describes the S & T diaspora in terms of actors and dynamics. The way it works through the Caldas network is presented in terms of an analysis of three major aspects : the electronic list through INTERNET, the local associations (network's nodes) and some joint projects between diaspora and the home community members. The concluding part draws the significance of the experience, its achievements as well as its limitations, and suggests some indicators and methods that could help develop it elsewhere. (Résumé d'auteur)