The Immigration Reform and Control Act of 1986 contains controversial provisions to allow temporary "replenishment" farmworkers to enter the United States to harvest perishable crops. This paper describes the role of legal and illegal foreign workers in California agriculture in relation to these provisions and the assumptions on which they rest. A 1983 survey of 1286 farmworkers in 37 California counties showed that 73% of all farmworkers were foreign. Citrus and other tree fruits had higher than average concentrations of foreign farmworkers (93% and 84%), while grapes had a below average concentration (67%). The relative concentration of illegal workers was (1) significantly above average for citrus, other tree fruits, and grapes, and significantly below average for field fruits and vegetables; (2) significantly above average for harvesting, tree thinning, and irrigating, and significantly below average for hoeing, crop sorting, operating machines, and serving as a foreman; and (3) significantly above average for southern San Joaquin valley and significantly below average for coastal and inland southern California. Compared to other regions, the San Joaquin valley had the highest unemployment rate and among the lowest hourly earnings for legal workers, suggesting that undocumented aliens may be displacing low skilled legal workers and depressing wage rates. This is contrary to growers' contentions, as is the lack of evidence that perishable crops depend more heavily on undocumented workers than other crops. The report contains 7 statistical tables, 13 references, and 21 related titles from the Urban Institute. (SV)