In the United States as well as in Western Europe, a combination of recession, nativist popular attitudes, and trade liberalization since 1980 has been accompanied by increasing immigration restrictions. This paper poses a singular question: Has the stiffening of U.S. immigration policy [by the Immigration Reform and Control Act of 1986 (IRCA), and subsequent policy decisions] reduced the volume and changed the composition and origins of Mexican undocumented migrants?Studies of national data show a reduction in such migration after IRCA. Using INS data on undocumeted entrants to South Texas, this paper documents Post‐IRCA increases in the proportions of migrants that are young, single, and male from metropolitan areas and from south central Mexico. These suggest that IRCA has served as a barrier inducing demographically selective migration and that changes in the Mexican economy since 1980 have favored the north versus the south–creating a “neo‐employment frontier” in the northeastern border states and a “neo‐migration hearth”in the Mesa Central and southwards.