National Super Alliance (Nasa) leaders on Wednesday said they questioned the inclusion of the National Youth Service nominal rolls into the voters register.
They complained that the names of young people who had enrolled with the youth service were listed as voters yet they had not sought registration.
The issue was raised at a meeting between officials of the electoral commission and the leaders.
Mr Raila Odinga said: "There are young people who worked with NYS but now when they go the registration centres they find their names already listed".
During the meeting, he called for an explanation from the commission.
Mr Odinga and Mr Musalia Mudavadi, Mr Kalonzo Musyoka and Moses Wetang'ula also asked why Biometric Voter Registration kits were lent to Burundi. They asked the commission to account for the material in foreign hands claiming it may be used to compromise the Kenya elections.
Sources close to the meeting at Mr Odinga's Capitol Hill Office said one of the commissioners explained that either all kits were configured to relay registration to the electoral commission's main system or someone at the commission's ICT department was manipulating the figures. They promised to investigate and protect the register.
The Opposition also called for fresh vetting of all electoral commission staff by the new commission before the elections.
The officials of the Independent Electoral and Boundaries Commissioner drove to Capitol Hill to meet Mr Odinga, Mr Mudavadi, Mr Musyoka and Mr Wetang'ula.
The previous day, they met President Uhuru Kenyatta at State House to discuss their state of preparedness for the elections.
Addressing a joint press conference after the two-hour meeting, Mr Odinga expressed the hope that the elections would be free and fair.
Electoral commission chairman Wafula Chebukati restated the commission's commitment to involve all stakeholders in the preparations to ensure successful elections.
Mr Odinga said Nasa leaders had presented a written memorandum to the commission, highlighting key issues they want addressed before the polls.
"We have a memorandum touching on the cleaning of the voter registers and the integrity of the roll among others, "Mr Odinga said.
Mr Odinga said the Opposition and the commission agreed on continuous meetings with all stakeholders.
"We have raised the issue of double registration and issuance of IDs that appear to favour the Jubilee strongholds,"Mr Odinga said. He added that some civil servants were being ordered to support the government in the voter registration which he said was unacceptable.
Mr Odinga's team also called for a review of the commission's ICT department, saying some of the officials were engaging in irregularities.
"We are seeking assurance in writing that the integrity of the register can be ascertained and that it is acceptable to all parties," the leaders said in their memorandum.
The Opposition wants the secretariat staff vetted and weed out compromised individuals.
They said they want details of the interface between the electoral commission and state organs including the Natinal Intelligence Service.
Nasa leaders raised doubts about the registration of births and deaths. They said that a briefing by the commission's chief executive, Mr Ezra Chiloba, to political parties on Tuesday made them suspicious about the records.
The memorandum said that Mr Chiloba had written to the registrar in November last year for an updated list of all deaths. The chief executive in his briefing, "claims that the registrar responded painting a very grim picture regarding the accuracy of their database on deaths especially."
Nasa also claimed they were under represented in the commission's infotech department making their contribution insignificant.
Mr Chebukati said there were anomalies in the voters register but that they were looking at every system.
"We agree there is a problem with the register but we are working on it," Mr Chebukati said.
Mr Chebukati however, said allegations that a former cabinet minister was manipulating the registers had not been reported to the commission.
"We are committed to deliver though we are a new team. We have had talks with the President and we have also met heads of missions to discuss various issues pertaining to the 2017 elections," Mr Chebukati said.