Former President Gerald Ford remained at the Mayo Clinic for unspecified tests on Wednesday, but officials wouldn't talk about his condition.

Ford was admitted Tuesday for tests and evaluation, according to Mayo Clinic spokesman John Murphy, who declined to elaborate. On Wednesday, Ford Chief of Staff Penny Circle said she wouldn't comment on the former president's condition.

Lee Simmons, a California friend of the 93-year-old former president, said on Tuesday that he heard that Ford was planning to undergo a series of tests for various "medical problems." He didn't have details but said he believed the tests had been planned in advance.

Ford spent a few days in Colorado's Vail Valley Medical Center last month because of shortness of breath. In January, he was hospitalized for 12 days in Rancho Mirage, Calif., to treat pneumonia. Five years ago, Ford suffered two small strokes and spent about a week in a hospital.

Ford became the nation's oldest living former president after the death of Ronald Reagan in 2004.

Ford was House minority leader when President Nixon chose him to replace the resigned Spiro Agnew as vice president in 1973. Ford became president on Aug. 9, 1974, when Nixon resigned amid the Watergate scandal.