"This is the largest temporary restroom event in the history of the United States," he said.

Don's Johns is providing many of the 5,000 port-a-potties for the inauguration, but there are other suppliers as well, such as Mr. John, Johnny Blue and Johnny on the Spot.

In all, there will be 5,000 port-a-potties from about 10 different vendors for Barack Obama's inauguration. On Thursday, they stood ready on the mall, port-a-potty-to-port-a-potty, some green, some blue, others gray.

The big question: will they be able to handle the call — er, nature's call — of the up to 2 million people?

"We think we've reached an appropriate number and can accommodate the crowds," said Kevin Griffis, a spokesman for the Presidential Inaugural Committee, a privately funded organization that is picking up the cost.

But Bill Line, a spokesman for the National Park Service, said there was really no way to say for certain.

"Ultimately, does anybody know how many people will show up?" he asked.

Line said that the Park Service recommends that organizers provide one port-a-potty for every 300 people, but stressed that it was up to the Presidential Inaugural Committee to decide whether to follow that. At that ratio, 5,000 port-a-potties would handle 1.5 million people.

For other large events, such as July 4 and the Cherry Blossom Festival, there are usually around 800 port-a-potties, Line said.

Harrell said that Don's Johns, based in Chantilly, Va., will have trucks on hand to handle any overflow situation, but attendants would hopefully pre-empt that by locking port-a-potties that fill up.

Organizers also point out that museums will be open for people to use bathrooms and escape from the cold. Griffis said the Presidential Inaugural Committee has paid the Smithsonian Institution $700,000 to open two of its museums, the National Museum of American History and the Smithsonian Castle, early at 8 a.m.

In addition, the Old Post Office Pavilion will open at 5 a.m. and close at 7 p.m. and the Ronald Reagan Building will be open 24 hours Tuesday, according to a news release by Eleanor Holmes Norton, Washington D.C.'s delegate to Congress.

Harrell was confident there will be enough port-a-potties. "Absolutely," he said. "Absolutely."