Second row forwards Charlie Matthews and Sam Twomey have agreed new contracts with Harlequins.
Former England U20 player Matthews made his debut for Quins in November 2009 and has gone on to make 101 appearances, playing in all 18 Premiership matches in 2015.
Twomey made his senior debut in 2011 against London Irish and has gone on to play 37 times for the club.
Harlequins director of rugby Conor O'Shea said: "The club is incredibly fortunate to have two players of Charlie and Sam's ability who still have so much growth and potential in them at 24 and 23 respectively.
"Alongside the other tight five forwards at the club I am sure they will learn and thrive from the presence of James Horwill and these two young men will be the corner stone of this club for years to come."
Matthews said: "I'm delighted to have committed to Harlequins, a club I've been associated with for 10 years. To have made my 100th appearance recently was a huge honour and I'm looking forward to continuing to learn and develop as part of this incredibly talented group for the coming years."
Twomey, who is expected to return from injury in March, said: "Harlequins is a club that strives to be successful every year and to be a part of that is something special. The club stands by its players and helps them progress to become the best they can be. I'm really pleased to have re-signed."