Two liberal groups – one of them directed by a brother of the Democratic Party chairman Howard Dean – will begin running a graphic attack advertisement Thursday morning raising questions about Senator John McCain’s health. Showing vivid and unflattering images of the fresh scar that appeared on Senator McCain’s face immediately after his last operation for melanoma skin cancer eight years ago, the commercial ends with a screen headline that reads, “Why won’t John McCain release his medical records?” (Mr. McCain, 72, did invite a limited group of reporters to inspect more than 1,100 pages of his medical records in May, though he gave them only a three-hour window in which to review the documents.)

The commercial is among the harshest to run against Mr. McCain yet, seeking to exploit the sensitive issues of health and age. Officials with the groups running the ad, Brave New PAC and Democracy for America, said they were only showing the spot initially on MSNBC over the next few days, a limited run intended to draw news media attention on a network that has increasingly catered to liberal tastes.

Officials at the groups, both of which are political action committees that rely on individual donors, said they hoped to show the spot on stations in battleground states in the coming weeks as well. But it is unclear if individual stations will accept the spot: Leighton Akio Woodhouse, a spokesman for Brave New PAC, said late Wednesday that CNN declined to accept the commercial after reviewing its contents this week.

The ad comes from the same two groups that recently released an advertisement questioning whether Mr. McCain’s time as a prisoner of war in Vietnam adversely affected his ability to lead.

Democracy for America has as its chairman Howard Dean’s brother, James H. Dean. Federal rules prohibit coordination between outside groups and campaigns or parties.

Daniel Medress, a spokesman for Democracy for America, said James Dean has not spoken with his brother about his activities at the group, which Howard Dean started in 2004. “We don’t coordinate with them,’’ Mr. Medress said of the Democratic National Committee, adding that at family dinners the Dean brothers, “sit there and make small talk, because they can’t talk about their jobs.”

Brad Woodhouse, a spokesman for the Democratic National Committee, said Howard Dean carefully follows all rules and regulations.

Brave New PAC is affiliated with California-based filmmaker Robert Greenwald, who runs several entities out of his “Brave New” office complex in Culver City; one of them, Brave New Foundation, a non-profit group that runs social issues campaigns, has as the chairman of its board Lawrence Lessig, a prominent Stanford Law School professor who has served as an informal adviser to Mr. Obama on technology policy issues.

Ben LaBolt, a spokesman for Mr. Obama, said the campaign had nothing to do with the spots and that Mr. Lessig had only advised Mr. Obama during the primaries, not in the general election. Mr. Woodhouse, the spokesman for Brave New PAC, said that Mr. Lessig is only affiliated with the Brave New Foundation, which operates in isolation from the political action committee. “There’s a fire wall there,’’ he said. “He has no relation to any of the projects we’re doing through the PAC.”

Danny Diaz, a Republican National Committee spokesman, said, “The fact that Howard Dean’s brother and an adviser to the Obama campaign are behind despicable and cheap smear ads against Senator McCain is deeply disappointing, but in no way surprising. Barack Obama has promised Americans an elevated debate offering nothing but gutter, Chicago-style politics.”

The spot opens with a photograph of Mr. McCain sporting a band aid over the scar on the left side of his face that caused by his surgery to remove the skin cancer in 2000, and the words, “John McCain is 72 and had cancer four times.”

One of two medical doctors featured in the spot, Dr. Michael D. Fratkin, says, “The relevance of knowing the details of his course with melanoma are very important.” He adds that another bout of cancer would “profoundly impact his capacity to lead.” The spot goes on to show two other unflattering pictures of Mr. McCain’s fresh scar.

In May, Mr. McCain’s doctors said he was in excellent health and that there was no recurrence of melanoma. That came at the same time that Mr. McCain’s campaign shared his medical records with reporters, though it restricted the review of 1,173 pages of documents to three hours by about 20 journalists who were not permitted to take photocopies. Outside experts had suggested that Mr. McCain’s initial prognosis may have been bleaker than his doctors had concluded, but Mr. McCain’s physicians said in May that they were heartened because the senator had gone seven years without another bout. They put the chances that the skin cancer would return at 10 percent.

(For more detail from those medical records and Mr. McCain’s prognosis, see this Times article from May.)

Officials with the groups said they were seeking a wider release of Mr. McCain’s medical records and defended the advertisement as raising legitimate issues about Mr. McCain.

“We think this is an election issue,’’ said Mr. Woodhouse of Brave New PAC. When asked why the groups chose to show such graphic imagery of Mr. McCain’s scars, Mr. Woodhouse said, “We have pictures of him with a scar to show that he has a history of surgery.”

The groups reported that they spent $50,000 to show the spot, $35,000 of it coming from Democracy for America and the remainder coming from Brave New PAC.