Maria Melendez swivels her hips, showing how she gets elderly citizens to get down in the weekly exercise class she teaches as a volunteer. Her husband, Miguel Melendez, smiles proudly in approval.

Apart from the accomplishment of their 53-year marriage, what keeps the electric pair, Ms. Melendez, 71, and her husband, 73, full of life is their devotion to helping others. 

Both came to the United States from Puerto Rico for better opportunities. They met in New York in 1950. She was 16 and living on the Lower East Side with relatives. He was two years older and living in the Bronx. "It was love at first sight," Mr. Melendez said. 

Despite Mr. Melendez's diabetes and failing kidneys - he has been on a transplant list for six years and undergoes dialysis three times a week - they spend their days making tracks across the Bronx to share some of their energy with elderly people down on their luck. 

For 37 years, Mr. Melendez was head cutter at H & R Hat Company in Manhattan, before his eyesight became too poor to operate machinery in 1987. That was when doctors determined that he had cataracts in both eyes.

But as time has advanced, the pair's endurance has hardly retreated. Over the years, the Melendezes, who have two grown children of their own, opened their home to 32 foster children.

"It's a heartbreaker," Mr. Melendez said. "You raise them to give them away."

These days, the couple works nearly every day. At the beginning of the new year, they were set up at the Douglas Leon Senior Center, located on the ground floor of a housing project in the South Bronx. A rotating Christmas tree in the corner seemed to be dancing slowly in comparison with Ms. Melendez, a comet of personality even at 8 a.m. She had spiky gray hair, and a purple T-shirt with gold lettering: "Crazy girls sexiest topless revue starring Pudgy!" 

Humming along to the Latin music in the background, she referred to the retirees who come see her once a month for blood-pressure readings as her "patients." 

She greeted each one and was quickly caught up with their lives before they become silent for Ms. Melendez to read their blood pressure. Mr. Melendez recorded the results. 

Ms. Melendez also counseled the senior citizens individually, telling some to show their doctor her reading. For one dapper older gentleman, the doctor's orders came straight from Ms. Melendez: "Your pulse is too fast. Leave the girls alone."

After a long day's work, the pair take the bus home to their apartment in Parkchester, where she cooks and likes to put on a record. They put up their feet - but not for long. Ms. Melendez loves to dance and sways to show how she and Mr. Melendez cut it up.

For the past 14 years, the Melendezes' volunteer work has been coordinated through the Retired and Senior Volunteer Program of the Community Service Society of New York, one of the seven charities supported by The New York Times Neediest Cases Fund. 

The Melendezes, who are retired, live on $600 a month in Social Security, after paying the rent. To meet their active transit costs, by bus and subway, the agency provided $199.50 in 2005 for transportation reimbursement, which it will continue to support.

To Ms. Melendez, that volunteer work is a vital part of life.

"I don't get bored," she said.