The richest Americans' share of national income has hit a postwar record, surpassing the highs reached in the 1990s bull market, and underlining the divergence of economic fortunes blamed for fueling anxiety among American workers.

The wealthiest 1% of Americans earned 21.2% of all income in 2005, according to new data from the Internal Revenue Service. That is up sharply from 19% in 2004, and surpasses the previous high of 20.8% set in 2000, at the peak of the previous bull market in stocks.

The bottom 50% earned 12.8% of all income, down from 13.4% in 2004 and a bit less than their 13% share in 2000.

The IRS data, based on a large sample of tax returns, are for "adjusted gross income," which is income after some deductions, such as for alimony and contributions to individual retirement accounts. While dated, many scholars prefer it to timelier data from other agencies because it provides details of the very richest -- for example, the top 0.1% and the top 1%, not just the top 10% -- and includes capital gains, an important, though volatile, source of income for the affluent.

The IRS data show that the median tax filer's income -- half earn less than the median, half earn more -- fell 2% between 2000 and 2005 when adjusted for inflation, to $30,881. At the same time, the income level for the tax filer just inside the top 1% grew 3%, to $364,657.