In what is an increasing disparity in finances, Munster have filled their roster with prop James Cronin, scrum-half Cathal Sheridan and centre Ivan Dineen.
Ulster have promoted from within, bringing in last year's Ireland U20 captain Niall Annett, current U20 Stuart Olding and prop Andy Warwick.
In the Amlin Cup, Leinster have added home-grown options in centre Brendan Macken, prop Jack O'Connell and flanker Dominic Ryan.
Former Munster scrum-half Peter Stringer has been added to the Bath squad for their tie with Stade Francais. HEINEKEN CUP
MUNSTER: James Cronin, Ivan Dineen, Cathal Sheridan
ULSTER: Niall Annett, Stuart Olding, Andrew Warwick
AMLIN CHALLENGE CUP
LEINSTER: Brendan Macken, Jack O'Connell, Dominic Ryan.