Limbaugh, whose syndicated radio program has a weekly audience of about 10 million, was reacting to Fox's appearance in  one of the spots for Missouri Democrat Claire McCaskill who is running against Republican Sen. James M. Talent.

    "He is exaggerating the effects of the disease," Limbaugh told listeners. "He's moving all around and shaking and it's purely an act. . . . This is really shameless of Michael J. Fox. Either he didn't take his medication or he's acting."

    As he speaks in the ad, Fox's restless torso weaves and writhes in a private dance. His head bobs from side to side, almost leaving the video frame.

    "This is the only time I've ever seen Michael J. Fox portray any of the symptoms of the disease he has," Limbaugh said. "He can barely control himself."

    "It's a shameless statement," John Rogers said Tuesday. Rogers, Fox's political adviser, who also serves on the board of the Parkinson's Action Network, added: "It's insulting. It's appallingly sad, at best."

    "Anyone who knows the disease well would regard his movement as classic severe Parkinson's disease," said Elaine Richman, a neuroscientist in Baltimore who co-wrote "Parkinson's Disease and the Family." "Any other interpretation is misinformed."

    Fox was campaigning Tuesday for Tammy Duckworth, a congressional candidate, outside Chicago, when he alluded to Limbaugh's remarks.

    "It's ironic, given some of the things that have been said in the last couple of days, that my pills are working really well right now," he said, according to a report on the CBS2 Web site.

    Later Monday, still on the air, Limbaugh apologized.

    "Now people are telling me they have seen Michael J. Fox in interviews and he does appear the same way in the interviews as he does in this commercial," Limbaugh said, according to a transcript on his website. "All right then, I stand corrected. . . . So I will bigly, hugely admit that I was wrong, and I will apologize to Michael J. Fox, if I am wrong in characterizing his behavior on this commercial as an act."

    Then Limbaugh went back on the attack saying: "Michael J. Fox is allowing his illness to be exploited and in the process is shilling for a Democratic politician."

    Limbaugh's shock at Fox's appearance is a measure of the disease's devastation, advocates say. Contrary to the charge that Fox might not take his medicine to enhance his symptoms, the medicine produces some of the uncontrolled body movements.

    "Stem cell research offers hope to millions of Americans with diseases like diabetes, Alzheimer's and Parkinson's," Fox says in the Cardin ad. "But George Bush and Michael Steele would put limits on the most promising stem cell research."

    Fox has appeared in ABC's "Boston Legal" this season. In his scenes, taped over the summer, Fox does not shake or loll his head as he does in the Cardin commercial, but does appear to be restraining himself, appearing almost rigid at times.

    A source with direct knowledge of Fox's illness who viewed the Cardin ad said Fox is not acting to exaggerate the effects of the disease. The source said Fox's scenes in "Boston Legal" had to be taped around his illness, as he worked to control the tremors associated with Parkinson's for limited periods of time.

    (Agencies)