FBI evidence technicians and others watched the hole carefully and inspected the dirt removed by the backhoe.
Crews dug for at least seven hours Thursday on the farm, which was once owned by a Hoffa associate. At least twice on Thursday, cadaver dogs were sent into the hole, but Dawn Clenney, a spokeswoman for the FBI in Detroit, said nothing significant was found.
The search was expected to continue through the Memorial Day holiday weekend.
Bill Koresky, whose company was hired by the FBI to knock down the barn and dig beneath it, predicted in a telephone interview Thursday night with The Associated Press that his company's digging would be complete on Friday.
He said the hole was 3 1/2- to 4-feet deep.
The farm once was owned by a Hoffa associate and is located not far from where the former Teamsters chief vanished in 1975. No trace of the Hoffa has ever been found, and no one has been charged in the case.
A government investigator said last week that Donovan Wells, who lived on the land at the time, was the one who gave the FBI the tip that has sparked the intense effort to solve a legendary mystery.
Wells' lawyer, Joseph J. Fabrizio, has said his client told the FBI in 1976 that he saw suspicious activity on the farm around the time of Hoffa's disappearance.
The investigator said that Wells wasn't that forthcoming 30 years ago and that he recently passed a polygraph exam. The investigator is familiar with the current dig and spoke on condition of anonymity because some of his information comes from records that have been sealed by a federal judge.
Another former lawyer for Wells, James Elsman, has said Wells said he actually saw a grave being dug with a backhoe. Elsman said that based on what Wells told him in 1976, he could pinpoint the location.
Hoffa last was seen on a night he was scheduled to have dinner at a restaurant about 20 miles from the farm. He was supposed to meet with a New Jersey Teamsters boss and a Detroit Mafia captain, both now dead.
Over the years, Hoffa's disappearance spawned endless theories — that he was entombed in concrete at Giants Stadium in the New Jersey Meadowlands; that he was ground up and thrown to the fishes in a Florida swamp; that he was obliterated in a mob-owned fat-rendering plant that has since burned down.