Ads from nursing mothers who want to earn money feeding other infants have popped up on Web sites, and urban agencies that offer household help say inquiries about wet nurses have soared from new mothers worried about contaminated infant formula.

Just a few decades ago, Mao Zedong denounced the practice of paying for wet nurses as decadent. And for decades after modern China's founding in 1949, nearly all women breastfed because they were too poor to buy infant formula.

But as China has grown more prosperous, many urban women have shunned breastfeeding for fear it would hurt their figures, or because they were seduced by rampant advertising that infant formula is nutritious, or even because grandparents of new infants clamor to take part in feeding rituals.

In the two weeks since a scandal erupted over adulterated infant formula and milk, tens of thousands of children have sought medical care, nearly 13,000 have been hospitalized, and four infants have died.

Zhan Liying, a 28-year-old mother who gave birth in early August, sat in a household employment agency Wednesday waiting for clients who might hire her to breastfeed their infant.

"With the infant formula issue, there is demand for wet nurses," Zhan said. "It's a way to make money."

In the city of Chengdu, one wet nurse offering her services for about US$40 a day told the China Daily newspaper this week that she'd gotten more than 30 telephone calls. The practice is legal.

Only prosperous Chinese families can afford it, though. Wet nurses often live with employers and charge anywhere from US$1,100 to US$2,700 a month.

Chinese law gives working mothers four to six months of maternity leave, although some career-oriented women prefer not to take such a leave.

"They are at the height of their careers. And they don't want to stay at home for months," said Lin Zhimin, a manager of the Beijing Harmony Trust Beauty Household Services Corp.

Anywhere from 40 percent to 65 percent of urban mothers in China rely at least partly on infant formula, according to surveys, although some suspect that the percentage is far higher.

Health Minister Chen Zhu acknowledged that changing lifestyles had a negative impact on breastfeeding.

"As we all know, young mothers are facing heavy pressure from the society. It happens often that mothers cannot breast feed babies enough because of their work. Due to that, it is true that the demand for infant formula in China is large," Chen said.

Infant formula producers advertise heavily and aggressively, often hiring doctors and health-care workers to help promote their formulas.

"It's a common belief in China that formula is more nutritious than breast milk," said Yanhong Wheeler, an author of parenting books and leader of La Leche League, a global nonprofit group that promotes breastfeeding. "It's a total lie. There's no way anyone can make a formula that can hold a candle to breast milk."

Some Chinese mothers believe they are unable to produce enough milk to feed their children. Others worry that breastfeeding will cause sagging.

Wet nurses were a staple of the imperial era. China's last emperor, Pu Yi, is known to have suckled the breast of his wet nurse into his teens.

Attitudes today remain ambivalent. A policewoman in Sichuan province, Jiang Xiaojuan, was proclaimed a heroine when she breastfed dozens of infants orphaned by the massive May 12 earthquake.

Some family members oppose the idea of feeding unrelated infants, causing some wet nurses to work on the sly.

On a wet nurse user forum on QQ, China's leading online social network, a man going by the nickname "blue forever," said he would block his wife from offering the service.

"Who likes other people's babies to suckle on the breasts of one's own wife?" he wrote.