The wife of Mexican President Vicente Fox has said she has no plans to run for the presidency when Mr Fox steps down in 2006.
Sahagun says she will work for the public good through her charity
Responding to growing speculation about her political ambitions, Martha Sahagun said that when her husband's term ended they would go home together.
Ms Sahagun also denied allegations that she had been involved in any decisions Mr Fox took in running his government.
Ms Sahagun has never formally declared an interest in the presidency.
But she is an active party campaigner and runs her own charitable foundation.
Last week presidential chief of staff Alfonso Durazo resigned, saying that the political ambition of the first lady had forced him to leave his post.
In a vitriolic public letter, Mr Durazo criticised her for meddling in state affairs and said Mexico was not ready for Mr Fox to leave the presidency to his wife.
A visibly irritated Ms Sahagun, dressed in bright red with matching lipstick, read out a brief statement at the presidential palace.
"Mexico is ready to be governed by a woman," she said.
"However, I will confirm that I will not be a candidate for the
presidency of the republic."
Sahagun says she never interferes with her husband's decisions
She said that she has a solid marriage and has never interfered with any decisions taken by her husband.
She then quickly left the podium, refusing to answer any questions.
Ms Sahagun, who was originally Mr Fox's press secretary, married him in 2001, the year after he became president.
She has previously refused to rule out running for the presidency.
The BBC's Claire Marshall in Mexico City says the drawn-out controversy has damaged the credibility of her husband.
Mexican newspapers poke fun at the couple, running cartoons with Mr Fox frequently depicted as his wife's lackey.
Her activism, especially with her charitable foundation Vamos Mexico, has also angered some within Mr Fox's own party, who complain she has an unfair advantage.
Despite her decision, our correspondent says, it is unlikely that Mr Sahagun will retire completely from the limelight.
She insists that she will continue to work towards the well-being of the community through her charity.