Data on the characteristics and labor market experiences of illegal aliens in the U.S. work force were collected by voluntary interviews with 793 apprehended illegal immigrants who had worked at least two weeks in the U.S. From the resulting diverse collection of case histories, it was concluded that (1) illegal workers in the U.S. are likely to be disadvantaged persons with little education and few skills and employed in low-level jobs (Most reported employment as the primary motive for migration and sent an average of $105 a month to their homeland to help support an average of 4.6 people); and (2) since illegal workers are successful in finding low-level jobs due to work experience in their own countries, and appear to be highly motivated and productive, an increasing supply of illegal aliens is likely to depress the educational and skill level of the workforce, depress labor standards in the secondary sector, cause displacement of low-skill legal resident workers, and create a new class of disadvantaged workers. Data are provided for the survey respondents on demographic characteristics, work experience, backhome socioeconomic conditions, reasons for migration, and on their contact with various governmental systems. U.S. immigration policy and practices are discussed, as well as the role and impact of illegals on the U.S. labor market. Appended to the report are results of another survey of illegal immigrants and the interview schedule. (NJ)