Venezuelan opposition leader Henrique Capriles has led hundreds of thousands of people on a march through the capital, Caracas, as he launches his candidacy for the presidency.
The 39-year-old walked and jogged with supporters Sunday to the National Election Council, where he formally registered as a candidate.
Capriles has vowed to create employment, fight crime and root out corruption, though most polls show him trailing President Hugo Chavez ahead of the election on October 7.
Capriles is the only opposition candidate selected to challenge the ailing president.
Chavez has said he plans to seek a sixth term despite being diagnosed with cancer. On Saturday, the president said recent medical tests following his cancer treatments show he is "absolutely fine." Chavez said the exams included imaging tests, which are used to check for the reappearance of tumors.
Chavez has yet to disclose specific details about his type of cancer.
He has traveled to Cuba several times to have tumors removed from his pelvic region and has undergone chemotherapy and radiation treatments.
His lack of transparency about his illness has fueled speculation about whether he will be strong enough to campaign.
The socialist leader said Saturday he has "faith in God" and his own will to live to "continue fighting" for Venezuela.
President Chavez will officially register as a presidential candidate Monday.
Some information for this report was provided by AP and Reuters.