This report examines several data series to test whether the employer sanctions mandated by the Immigration Reform and Control Act (IRCA) of 1986 have reduced the flow of undocumented immigrants to the United States. Specifically, the authors use apprehensions--failed attempts to enter the United States--and counts taken by the Colegio de la Frontera Norte of illegal crossings at Canyon Zapata in Tijuana as measures of the flow of people who attempt to cross the border illegally. In the case of apprehensions, they predict post-IRCA apprehension levels using a model estimated with pre-IRCA data and compare predicted with actual levels to test for a drop after accounting for declines in attempted crossings due to the legalization of undocumented immigrants provided for by IRCA. Significant declines in either of the measures, assuming all other factors remained the same, signal employer sanctions may be having an effect. The authors also examine statistics on immigration visa waiting lists, tourist visas, and applications for asylum for evidence of changes in the behavior of potential undocumented immigrants. The economic indicators include a wage survey designed to detect changes in employment patterns stemming from the law and an examination of applications for foreign workers under the H-2A program. The authors find that alone, none of their datasets provides conclusive evidence that employer sanctions have or have not reduced undocumented immigration. Together, the preponderance of the evidence points to some decline in the flow.