emigration rates of tertiary educated workers for 61 developing countries. These estimates are based on three main statistical sources (US Census data on the skill structure of immigration, OECD data on immigration per country of origin, Barro and Lee (2000) data describing the skill structure in sending countries). They had to rely on a set of assumptions. First, for non-US countries, they use OCDE migration statistics which report limited information on the origin of immigrants<sup>4</sup> . Second, they transpose the skill structure of US immigrants on the OECD total immigration stock. For example, migrants from South Africa to Great Britain are assumed to be distributed across educational categories in the same way as migrants from South Africa to the United States. This assumption is particularly tentative for countries which do not send many migrants to the United States. Adams (2003) used the same methodology to update the emigration rates of 24 labor-exporting countries in 2000. Beine et al (2003) used Carrington and Detragiache’s data to predict the growth impact of the brain drain. Yet, given the assumptions, the evidence concerning the consequences of skilled migration for developing countries remains not only limited but also largely inconclusive.

The purpose of this paper is to build an exhaustive international database on the brain drain describing the loss of skilled workers for all developing and developed countries. The majority of high-skilled workers go to industrialized countries. Building on Carrington and Detragiache (1998) and Adams (2003), we focus on the South-North and North-North brain drain. We are aware that a brain drain can be observed outside the OECD area (migration of skilled workers to the Gulf countries, South Africa, Malaysia, Hong-Kong, Singapore, Taiwan, etc) but, at this stage, we do not take these ‡ows into account<sup>5</sup> .

We collected data on the immigration structure by educational attainment and country of birth from all OECD receiving countries. Census and register data are (or will be) available for about 25 countries in 2000 (out of 30 OECD countries). To allow comparison between 1990 and 2000, we consider the same number of receiving countries in 1990 (even if six of them were not members of the OECD). Census data are (or will be) available for about 18 countries in 1990. Survey data and reasonable assumptions can be used to evaluate the structure of immigration in the remaining countries.

In this release of the database, we also use survey data for countries in which the Census is not yet available in the desired format (i.e. for 12 European countries). At this stage, we estimate that we are able to characterize the country of birth and the educational attainment of 92.7 percent of the OECD stock of adult immigrants in 4 OCDE statistics su¤er from various limitations (see OCDE, 2002) . For example, they only provide information on the country of origin for the the main sending countries. In 2000, they are not avalaible for Greece, Iceland, Mexico, Slovakia, Turkey.

> 5According to the United Nations (2002), migration to developed countries represented 53 percent of the world migration in 1990 and 60 percent in 2000. High-skill migration is even more concentrated. In this study, we estimate that about 85 percent of high-skill migrants go to OECD countries.

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