WASHINGTON - Men with larger foreskins are more likely to become infected with the AIDS virus, researchers said Wednesday in a finding that helps explain why circumcision can protect men.

The study of 965 men in Uganda, all without AIDS at the start, showed those with larger foreskins were more likely to become infected.

Infection rates correlated with the size of the foreskin, Dr. Godfrey Kigozi of Johns Hopkins University's Rakai Health Sciences Program in Uganda and colleagues found.

"Mean foreskin surface area was significantly higher among men who acquired HIV," they wrote in the journal AIDS.

Several studies have shown that circumcision -- removal of the foreskin -- can protect men, but not their female sex partners, from HIV. It does not completely prevent infection but reduces the risk.

Researchers believe the foreskin has many immune cells called dendritic cells, which may provide a route into the body for the virus.

Kigozi's team looked at men getting circumcised for one of the studies in Uganda.

"The surface area of the foreskin was measured after surgery using standardized procedures," they wrote.