Infection with an apparently harmless, newly recognized virus seems to interfere with HIV, slowing its progression and prolonging survival of AIDS patients.

What isn't known is exactly how the virus, called GBV-C or hepatitis G, inhibits HIV. Researchers say if they can figure that out, it could lead to new treatments for AIDS virus.

In the meantime, they warned patients against intentionally infecting themselves.

"If we can identify the path GBV-C is taking to inhibit HIV, then we're well on the way to making this something practical," said one of the researchers, Dr. Jack Stapleton of the Iowa City Veterans Affairs Medical Center and the University of Iowa.

The findings were reported in two studies in Thursday's New England Journal of Medicine. They confirm earlier, smaller studies that showed that patients with both HIV and hepatitis G lived longer than those infected with HIV alone.

The hepatitis G virus, discovered in 1995, does not appear to cause hepatitis or any other disease, unlike other blood-borne hepatitis viruses that cause liver damage. It is found in about 2 percent of healthy blood donors.

The Iowa study looked at 362 HIV-infected patients treated between 1988 and 1999. About 40 percent, 144 patients, were also infected with hepatitis G.

About 29 percent (41 patients) of those infected with hepatitis G died during four years of follow-up, compared with 56 percent (123 patients) who were not infected with hepatitis G.

Researchers calculated that HIV-infected people without the hepatitis G infection were nearly four times more likely to die than those with both infections during the four-year period.

A second study of 197 HIV patients conducted at Medical School Hanover in Germany also found significantly longer survival for the 33 HIV patients with hepatitis G, even after more potent AIDS drugs became available in 1996. Researchers also tested hepatitis G-infected blood and found the more hepatitis G infection, the less HIV was in the blood.

"We don't have any clues how it works at the moment, but I'm quite confident that we will gain this information in the next 12 months," said Dr. Hans L. Tillmann, one of the researchers.

The German researchers did one of the earliest studies that showed that hepatitis G may be beneficial for HIV patients. Tillmann said they were trying to determine whether GBV-C had the same negative effect as hepatitis B and C on people with HIV, but found the opposite.

Dr. Steven Wolinsky of Northwestern University Medical School, co-author of an accompanying editorial, said the findings of the two studies need to be kept in perspective.

"While we're looking at larger numbers of patients, we still don't really have a specific mechanism, nor have we ruled out any other potential variables that may be responsible," Wolinsky said.

Tillmann and Stapleton both strongly warned against intentionally infecting HIV patients with hepatitis G while research continues, a warning echoed by Wolinsky.

"We don't really know what the long-term consequences of infection with this virus is," Wolinsky said. "We also know that it seems to travel with other viruses, and we don't know if it's an accidental tourist or not."