England Lions batsman Alex Lees and seam bowler Steve Patterson have signed new contracts with champions Yorkshire.
Lees, 21, has committed his future to the club until the end of 2019 and Patterson has agreed a deal until 2016.
"The sign of a great side is to be successful over a period of time," Lees told the club website.
"We have to build on what we achieved in 2014 and hopefully go on to dominate the Championship. The new campaign will be a test of our mental strength."
He scored 971 runs in last summer's Championship at an average of 44 and his successful opening partnership with Adam Lyth was a major factor in Yorkshire winning the title for the first time since 2001.
Lyth, 27, signed a new contract with Yorkshire last week, which will run until 2018, and he, together with Lees, was selected for the Lions winter tour to South Africa.
Patterson, meanwhile, has taken 231 first-class wickets at an average of 28.18 since making his debut in 2005, including 36 in the Championship last summer.
"I want to continue contributing to the team with solid performances," the 31-year-old said.
"We have a tight unit and we know after winning the Championship last year we are going to have to improve our game further to retain the title."
Yorkshire begin their title defence with a trip to New Road to face promoted Worcestershire, starting on 12 April.