Munster have signed hooker Rhys Marshall in a three-year deal while Thomas du Tiot and Cathal Sheridan have joined on three-month contracts.
Former New Zealander U20s front-row Marshall moves to Munster from Super Rugby side the Chiefs and plays for Taranaki in the Mitre 10 Cup.
Sharks prop du Toit arrives in a loan agreement, while scrum-half Sheridan returns to the Irish province.
Munster are second in the Pro12 standings, two points behind Ulster.
UL Bohemians player Sheridan left Munster in May following a three-year spell with the Thomond Park team.
The deals for Marshall and du Toit are subject to the players being granted a valid work permit.
"In certain positions we had to look at our short-term and long-term options in making sure we had adequate cover," said Munster director of rugby Rassie Erasmus.
"We are about to head into a fully loaded schedule across Europe and the Pro12 and needed to build on our depth in a few key areas so these short term contracts will help in that regard.
"Additionally with injuries to Mike Sherry and Kevin O'Byrne, Rhys Marshall will help in the immediate future and looking beyond that he is a talented long-term prospect for such a pivotal position within our squad."