A federal probe of tainted Chinese drywall has broadened because a small number of homeowners are reporting that American-made drywall is causing some of the same problems: a sickening, sulfurous stench and corroded pipes and wiring.

"We are not limited in the scope of our investigation to just Chinese drywall," said Scott Wolfson, spokesman for the Consumer Products Safety Commission, which is conducting the largest investigation in its history after thousands of homeowners complained and filed lawsuits.

The vast majority of complaints still center on China-made gypsum board imported during the recent U.S. housing boom, when domestic building materials were in short supply. And the commission's investigation is focused mainly on the imported drywall, Wolfson said.

But sporadic reports are surfacing from owners of homes built with American drywall, and the symptoms they report are similar to those reported with the Chinese drywall: a rotten-egg odor that makes occupants sick, corrosion of copper pipes, and ruined TVs and air conditioners.

"We've got a huge problem here, and we just need help," said George Brincku, 48, who bought his southwest Florida house in 2004 and almost immediately began noticing the odd smell, the corrosion of wires and headaches.

When he saw reports about Chinese drywall, he assumed that was the problem with his house until he called the contractor who installed it.

"I have all 100% American-made drywall," Brincku said.

He sent samples to the Massachusetts Institute of Technology, which found that the wallboard from Brincku's home contained 50% gypsum and 50% cellulose, an organic compound. Drywall should contain mostly gypsum.