Trucks supplying Nato in Afghanistan crossed the border from Pakistan for the first time in seven months after Islamabad reopened transit routes.
Pakistani officials said three Nato containers cleared for transit passed through the Chaman point on Thursday.
Many more lorries remain in the southern Pakistani port of Karachi awaiting instructions to proceed.
Pakistan reopened the routes after the US apologised for killing 24 of its soldiers on the border in November.
The decision will save the US hundreds of millions of dollars as it prepares to withdraw from Afghanistan.
Pakistan has said it hopes the move will improve relations with the US and other Nato countries.
"We received orders yesterday to allow Nato supply trucks through, but security officials hadn't received their instructions. They received their orders today," Pakistani customs Imran Raza told Reuters news agency.
The Associated Press of Pakistan said: "At least three containers carrying supplies for Isaf forces crossed into Afghanistan on Thursday morning, officials confirmed."
Fazal Bari of Pakistan's Frontier Constabulary told the BBC's Urdu service the first truck to cross was carrying water and food. It was greeted by Afghan officials at Spin Boldak on the other side.
However, most Nato trucks in Pakistan are still parked up in Karachi and other places - it appears they remain stationary for now, the BBC's Aleem Maqbool reports.
Our correspondent, who is in Karachi, says drivers there have yet to be given the all-clear and told the BBC they knew of no trucks leaving the city as of Thursday morning.
The seven month-long row over supply lines have been hugely damaging to relations between Pakistan and the US, with both sides unwilling to back down.
It began in November last year when two dozen Pakistani soldiers were killed as US air strikes hit two posts on the Afghan border.
At the time, Afghan officials said that Nato forces had been retaliating for gunfire from the Pakistani side of the volatile border, but Pakistan rejected that claim.
The supply route through Pakistan is crucial to the United States as it prepares to pull all combat troops out of Afghanistan by 2014.
Reports suggest the US may now release over $1bn in funding to Pakistan's military.
Islamabad confirmed it would not raise transit fees when the lines re-open.
US officials say the existing charge of $250 (£160) per truck will not change - Washington had baulked at a reported Pakistani demand for $5,000 per container to let supplies flow again.
The Taliban have threatened to resume attacks on the convoys.