The Queen has fulfilled a long-held ambition to watch the famous Kentucky Derby horse race in the US.
The Queen, who is a keen racing enthusiast, has visited Kentucky four times before but not been to the race.
She and the Duke of Edinburgh, who are touring the east coast of the US, watched Street Sense win the race.
Workers at the course at Churchill Downs, Louisville, have had etiquette lessons, and a special menu has been prepared for the royal visit.
The Queen was accompanied by the Duke of Edinburgh and close friend horse breeder William Farish, a former US ambassador to the UK, whose farm she was staying on.
She watched the event from the course's Stakes room. At one point she was spotted on the room's balcony watching the eighth race of the day, the Humana Distaff.
Flanked by the Duke of Edinburgh and Mr Farish, she was beaming broadly and wearing her glasses.
The Queen also viewed the Derby trophy which has an upside down horse shoe on the front.
Jay Ferguson, the keeper of the trophy, said: "She said 'It keeps the luck in' and that's right.
"She seemed to be enjoying herself."
Race course president Steve Sexton said: "Queen Elizabeth is certainly the most prestigious guest we've entertained in the modern-day history of the Kentucky Derby."
Meanwhile, the Queen's carbon footprint will be calculated and offset for the first time for a state visit.
Buckingham Palace will make a donation to an environmental charity to offset the plane journeys made by the Royal couple and their entourage.
On Monday, the Queen will meet President Bush and first lady Laura Bush in Washington DC where a state dinner will be held.
The following day the Queen and Mrs Bush will visit the Children's National Medical Centre in Washington.
The Queen and the Duke of Edinburgh have already been to the site of the first permanent English settlement in the US, Jamestown in Virginia, to mark its 400th anniversary.
Following her arrival at Virginia's Richmond Airport, the Queen extended her sympathies to those affected by the shootings at Virginia Tech last month, and spoke of the strong bonds between the US and the UK.
THE QUEEN'S FIRST CARBON-OFFSET STATE VISIT
Total air miles
- 13,317 km or 8,275 milesAmount of CO2 emitted based on scheduled flights
- 1. 5 tonnesEstimated offset cost per person
- £13.20 to £14.18 ($26.22-$28.17) depending on type of offset package
Source: The Carbon Neutral Company carbon calculator