Senior government officials have claimed that in recent years an average of 1.4 million illegal aliens have entered the United States annually without apprehension. This conjectural figure does not take into account the fact that the net flow of immigrants is always less than the gross flow. In this paper, seven estimates are made concerning the net flow of undocumented Mexican immigrants to the United States in the period 1970–1975. These estimates are based on the growth of the population of Mexican origin according to the Current Population Survey. According to these estimates the annual net flow ranged from 82,300 to 232,400 persons.