Two billboards by the People for the Ethical Treatment of Animals depict Giuliani wearing a milk mustache and asking: "Got prostate cancer?" The ad claims a connection between drinking milk and prostate cancer, for which the mayor is being treated.

"It's tasteless and inappropriate to exploit my illness and also takes advantage of my position as the mayor for advertising purposes," Giuliani said Thursday. "The message they're trying to deliver just makes sense in their own zealous, out-of-control thinking."

Giuliani said he was considering suing PETA because the organization was using his image in an advertisement without his permission.

A study by the Harvard School of Public Health in April raised the possibility that consuming lots of milk and other dairy products could modestly increase the risk of prostate cancer. The study stressed the case was far from settled and recommended further study of calcium's effects on health.

PETA targeted Wisconsin for the ad because it's "America's Dairyland, so it seems to be the perfect place to bring the message that dairy products are horrible for human health, catastrophic for the environment and a living nightmare for these cows and their veal calf babies," said Bruce Friedrich, the group's vegetarian campaign coordinator.

New York City Mayor Rudy Giuliani says his prostate cancer was not caused by milk.

The milk industry pointed out that other research suggests dairy products help fight high blood pressure, colon cancer and osteoporosis.

"True to form, it's their typical insensitive way of misleading the public for their own gain," said Debra Wendorf Boyke, spokeswoman for the Wisconsin Milk Marketing Board.

The animal-rights group has pulled previous ads that incited controversy. A PETA ad campaign that urged college students to drink beer instead of milk was pulled last spring because of objections by Mothers Against Drunk Driving.