Queen's University speedster David McIlwaine comes in at full-back for Jamie Smith, who sustained an eye injury against Bath.
Craig Gilroy and Nevin Spence replace Mark McCrea and Tommy Seymour on the wings, and Niall O'Connor and Ian Porter are the starting half-backs in place of Ian Humphreys and the injured Paul Marshall (shoulder).
Up front, experienced prop Bryan Young has been named in the starting line-up having recovered from a hip injury which caused his late withdrawal from the squad last week.
Declan Fitzpatrick retains his front row position, and Andi Kyriacou is in at hooker instead of Nigel Brady.
Stand-in captain Johann Muller's partner in the second row this week is Ryan Caldwell, while the only change to the back row is the inclusion of Thomas Anderson at openside flanker.
ULSTER (v Harlequins): David McIlwaine; Craig Gilroy, Darren Cave, Ian Whitten, Nevin Spence; Niall O’Connor, Ian Porter; Bryan Young, Andi Kyriacou, Declan Fitzpatrick, Johann Muller (capt), Ryan Caldwell, Pedrie Wannenburg, Thomas Anderson, Robbie Diack.
Replacements (from): Nigel Brady, Paul Karayiannis, Adam Macklin, Tim Barker, Neil McComb, Michael Heaney, Ian Humphreys, Luke Marshall, Jonny Shiels, Mark McCrea.