Explanation of shifts in U.S. Congressional representation among states have often overlooked the effects of international migration on the size and distribution of the U.S. population. Seventy percent of recent U.S. immigrants have settled in California, New York, Texas, Florida, New Jersey, and Illinois. Estimates of the distribution of immigrants from 1950-1980 indicated that these six states had 16 more Congressional seats in 1980 than they would have had in the absence of immigration. California gained six seats through immigration, which represented 40 percent of its total representation increase. With a net immigration of 450,000 persons yearly, the six major immigrant receiving states will increase their share of Congressional seats from 161 in 1985 to 179 in 2010, with seven of these 18 added seats attributable to immigration. A net immigration number of 750,000 yearly would enable the six receiving states to increase their share over the next three decades to 184, 12 seats more than they would have had without immigrant settlement. California would gain the largest number of Congressional seats as a result of either projection, receiving by 2010 four seats through an annual immigration of 450,000 or seven seats if immigration is 750,000 per year. Tables and graphs are included. (Author/JHP)