Abstract. Domestic citation to papers from the same country and the greater citation impact of documents involving international collaboration are two phenomena that have been extensively studied and contrasted. Here, however, we show that it is not so much a national bias, but that papers have a greater impact on their immediate environments, an impact that is diluted as that environment grows. For this reason, the greatest biases are observed in countries with a limited production. Papers that involve international collaboration have a greater impact in general, on the one hand, because they have multiple “immediate environments,” and on the other because of their greater quality or prestige. In short, one can say that science knows no frontiers. Certainly there is a greater impact on the authors' immediate environment, but this does not necessarily have to coincide with their national environments, which fade in importance as the collaborative environment expands.