Northern Ireland's Michael Dunlop topped the Superbike times in the opening Southern 100 practice session on Monday.
The defending solo champion lapped the Billown course at a speed of 109.573mph on Honda machinery.
Fourteen-time winner Ryan Farquhar was next quickest (107.035) with the all-time leading rider at the event Ian Lougher third fastest.
Lougher posted the quickest time on a 600cc machine.
The Welsh rider is the most successful rider in the event's history with 32 wins, one more than Joey Dunlop.
Meanwhile, Tim Reeves and Dan Sayle set the quickest sidecars lap of the evening and Chris Palmer tops the 125/400cc class.
Farquhar posted the best time of the session in the 250/650cc class.
The Billown meeting dates back to 1955 and sees competitors from all over the United Kingdom take on the 4.25-mile circuit in the south of the island.
Organisers say the event is in "great health," with 32 newcomers signed up to compete this week.
Spokesman Phil Edge said: "It is great to attract so much new interest and we are expecting some great battles."
Practice will continue on Tuesday evening, followed by the first of 13 races.