Kadima MK Shlomo Breznitz handed in his resignation to Knesset Speaker Dalia Itzik on Tuesday morning.
In the letter, he wrote that only reason he quit was because at the age of 71, he wanted to focus the rest of his life on his company, which he founded eight years ago. He said it had been an honor to serve in the Knesset, but "I need the company more than it needs me."
He said that he had loved a good portion of his work in the Knesset and was thankful to Prime Minister Ehud Olmert for giving him the opportunity.
Breznitz will be replaced in the Knesset by Kadima Director-General Yohanan Plesner, a Harvard graduate who is close to Olmert.