Aidan O'Brien has already made hay in many of the classic trials so far this season but Macarthur can make the biggest impression of all in what is arguably the most important Derby trial of all at Leopardstown tomorrow.
The champion trainer saddles four of the six runners in the Derrinstown Stud Derby Trial which has thrown up the Epsom heroes Sinndar (2000), Galileo (2001) and High Chaparral (2002) already this decade as well as other top-class horses such as Yeats and Alamshar.
It is expected to be a significant Epsom pointer this time too and if Macarthur can win impressively, then he looks almost certain to head the Derby ante-post betting by the end of the weekend.
Macarthur is already as low as 8 to 1 second favourite behind Authorized who runs in next week's Dante at York and that position is no doubt puzzling to those strict form-book students who will have Mores Wells two lengths clear of the O'Brien horse on Ballysax running over the course and distance last month.
Kevin Prendergast's colt is again in opposition alongside Dermot Weld's maiden Westlake and the rest of the O'Brien team which includes the Guineas 11th Yellowstone.
Mores Wells is twice Macarthur's odds for Epsom despite having won the Ballysax, and possibly the most informative maiden of the season so far, and he is clearly a horse still on the up.
But Macarthur was making his seasonal debut last month and wasn't knocked around when it became obvious he wasn't going to get to the winner.
The dark horse looks to be Archipenko who will be ridden by Michael Kinane as he makes his first start of 2007.
Kinane will also be a major player in the Group Three 1,000 Guineas Trial on board the fast-ground loving Xinji.
Finsceal Beo might be the outstanding three-year-old filly in Europe right now but this should still be an ultra-informative contest with Gaudeamus, whose saddle slipped in Monday's Athasi, conceding weight all round and highly-touted prospects such as Thiella stepping up to pattern level.
Xinji falls into that category and the John Oxx team will be hoping any rain stays away this weekend for this filly who impressed at Gowran last season.
Danak represents Oxx and Kinane in the Group Three Amethyst Stakes which looks an intriguing four-runner contest.
Danak edged out Decado and Quinmaster on his last start and while the others will fancy their chances for revenge, their should still be improvement in Danak who is unbeaten in four to date.
The feature on day one of the Killarney May festival is the €70,000 Murphys Irish Stout Handicap Hurdle and with the Punchestown runner-up Holly Tree topping the ratings, it looks to have left Andrew Leigh's progressive mount Phantom Lad in with a winning weight.
Pacolet can make it four in a row by winning the ladies race under Adrienne Foley and Caman Swinger looks the one for the bumper.
Today's home action is a mixed-card at Downpatrick where the in-form Pat Flynn sends Bahrain Storm north for the mile and a half conditions race. Dermot Weld's Ballinrobe winner Vision Of Grandeur boasts an 86 rating but Bahrain Storm looked an improved runner over flights during the spring.
