June 24, 2004 -- While commercials and Web sites have joked about reaching the "end of the Internet," many businesses may not find it so funny to know that the U.S. may be nearing a limit in the number of people actually interested in logging on.

A survey of 26,000 people, conducted by Mediamark Research Inc., found regular use of the Internet - defined as use in the past 30 days - has leveled off at 63 percent of the adult U.S. population. This marked an increase of only 1.7 percent for the 12-month period ended April 2004. MRI concluded that growth is being stunted by an "entrenched group of non-connected adults and a diehard group of resistors."

Strongest growth was seen between 1999 and 2000, when the number of adults logging on increased 11.3 percent.

Almost 80 percent of the adult U.S. population has regular access to the Internet, either at home, work or another location, says MRI. The remaining 20 percent of the population are the "un-connected." However, 20 percent of those with access are "resistors," or those who refuse to use it.

Most growth in users normally comes from the unconnected, according to MRI. But, as the pool has shrunk, what's left is an older, lower-income and ethnically-diverse group, which has proven more difficult to get online.

The median income of unconnected adults is $19,571, compared to an adult population average of $33,144. Additionally, MRI found that the unconnected are far more likely to be African-American and Hispanic. Almost 15 percent of the unconnected speak mostly or only Spanish at home.

"Substantial growth in the Internet-using population is unlikely to resume without cheaper Internet connections, more Spanish-language Internet provider services and, perhaps most important, compelling new reasons for non-users to switch sides," said Andy Arthur, vice president of client services at Mediamark.