Belzer, who plays Detective John Munch on "SVU," appears in the ad with a pup named Munch and a kitten name Tater Tot, both from the Little Shelter Animal Adoption Center, the New York Daily News reported Monday.
"I had the greatest time. It was wonderful," Belzer told the newspaper. "Whenever a dog comes into a room your blood pressure goes down."
More than 2,000 taxi cabs as well as newspapers and magazines will carry the ads, the Daily News said.
Belzer, 61, said he had a pet turtle as a kid and has had seven cats through the years, but is now just learning the tricks of being a dog owner.
He recently adopted a 10-month-old border collie-mix who rescued in France. He named the pup Django after jazz great Django Reinhardt.
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