A longitudinal analysis encompassing the period 1946 through 1965, relates the changes in migration rates of illegal migrants from Mexico to the United States to changes in certain predictor variables (farm wages and agricultural productivity in both the U.S. and Mexico, agricultural commodity prices in Mexico, and rate of capital investment in the U.S.). The flow of illegal Mexican aliens was found to be clearly affected by changes in the relative vigor of agricultural enterprise in the two countries. (EH)