This paper contributes to the literature on the semi -strong efficiency concept. It studies the impact of exogenous information circulated by the media on stock prices. It brings the exogenous information coloration closer to its underlying asset in order to analyze variation in stock prices. Empirical tests show that information makes anticipating price evolution possible. Moreover, it challenges the foundations of efficiency. Results show that predicting stock returns in the short term is possible. JEL codes: C14, D83, G14