De Castro, who will be casting his ballot in Barangay Culiat in Tandang Sora, Quezon City, reminded voters of the responsibility that comes with the right to suffrage.
"Dapat sa ating pagboto ay isipin natin na nakasalalay ang kinabukasan ng ating bayan dito (In voting, we must bear in mind that the future of the country is at stake )," said De Castro, President Arroyos running mate under the Koalisyon ng Katapatan at Karanasan para sa Kinabukasan (K-4).
He urged voters to expose those involved in "dagdag-bawas" (vote padding and shaving). "Bantayan natin ang ating boto (Let us guard our votes)," he said.
A popular broadcaster before joining politics, De Castro is widely seen to win the vice presidential race, a latest survey of the Strategic Forecasting Inc. (Stratfor) reportedly showed.
The poll, conducted April 20 to May 5, showed De Castro leading with a 35.2 percent rating, or equivalent to 10.5 million votes.
The report on the Stratfor survey results did not mention the name of De Castros chief opponent, Koalisyon ng Nagkakaisang Pilipino (KNP) vice presidential contender Sen. Loren Legarda. It only said De Castros "closest rival" got a 24.1 percent rating among 7,000 respondents nationwide from classes A to E.
The Stratfor survey, reportedly commissioned by the United States Embassy, has a margin of error of plus or minus two percentage points.
De Castro reacted to the report by saying, "This should dispel any doubts about the real standing in the fight for the vice presidency."
He expressed belief he will win by a large margin in todays polls.
"Pinapakita lang ng survey na ito na matatalino ang ating mga mamamayan at hindi mgpapadala sa paninirang isinagawa sa aking pagkatao, reputasyon at maging sa aking pamilya (This goes to show that the people are intelligent and are not easily swayed by the intrigues hurled at my being, reputation and to my family)," said De Castro, who has recently been a target of controversies.
On the other hand, supporters of Legarda believe she will trounce De Castro, her former colleague in the broadcasting industry and in the Senate.
KNP spokesman Mike Romero noted that support from various sectors of society has been pouring in for Legarda, running mate of popular movie actor Fernando Poe Jr.
Yesterday, the president of the laymens association of the Aglipayan Church endorsed Legardas bid.
Pete Pico, head of the Philippine Independent Churchs national laymen association, urged "all peace-loving and God-fearing Filipinos to bring back righteousness in governance" by voting for Legarda.
Her supporters also noted that Legarda draws support from Muslim leaders and other religious groups like the charismatic El Shaddai movement.
"Shes a unifying force," Pico said. "A vice president destined to relegate to the dustbin of history the notion that VPs are nothing more than spare tires."
De Castro and Legarda were stablemates at ABS-CBN, the countrys largest broadcast network.
Unlike De Castro, Legardas term as senator ends in June this year, a month after the elections. She would be out of public office if she loses in the vice presidential race.
Legarda topped the senatorial race in 1998, garnering more than 15 million votes. De Castro topped the Senate race in 2001, and his term ends in 2007.
In the latest opinion survey of the Social Weather Stations (SWS) released Saturday, De Castro leads Legarda although the margin has been reduced to four percent or 43 percent against 39 percent.
The poll also showed the President pulling away from Poe, getting 37 percent of the votes compared to 30 percent for her rival.