Since the credit crisis started shaking the world financial markets this summer, many professional traders have taken big losses. Another, less likely group of investors has, too: middle-class Japanese homemakers who moonlight as amateur currency speculators.

Ms. Itoh is one of them. Ms. Itoh, a homemaker in the central city of Nagoya, did not want her full name used because her husband still does not know. After cleaning the dinner dishes, she would spend her evenings buying and selling British pounds and Australian dollars.

When the turmoil struck the currency markets last month, Ms. Itoh spent a sleepless week as market losses wiped out her holdings. She lost nearly all her family’s $100,000 in savings.

“I wanted to add to our savings, but instead I got in over my head,” Ms. Itoh, 36, said.

Tens of thousands of married Japanese women ventured into online currency trading in the last year and a half, playing the markets between household chores or after tucking the children into bed. While the overwhelmingly male world of traders and investors here mocked them as kimono-clad “Mrs. Watanabes,” these women collectively emerged as a powerful force, using Japan’s vast wealth to sway prices and confound economists.

Many bought and sold stakes worth into the millions of dollars through margin trading, a potentially lucrative but risky form of trading that uses borrowed money.

Until the credit crisis, which began with troubles in the American mortgage market, the value of foreign currencies traded online by private Japanese citizens, including women, averaged $9.1 billion a day — almost a fifth of all foreign exchange trading worldwide during trading hours in Tokyo, said Kazuhiro Shirakura, an analyst at the Yano Research Institute in Tokyo.

Now Japan’s homemaker-traders may become yet another casualty of the shakeout hitting the debt, credit and stock markets worldwide. If so, these married women could lose more than just an investment opportunity. They could also lose the newfound economic freedom that drew many to currency trading in the first place.

Most analysts estimate that Japanese online investors lost $2.5 billion trading currency last month. In fact, the subprime-mortgage crisis was the first severe market downturn since online trading took off here. Economists see the current tumult as the first real test of Japan’s homemaker-traders, and whether these newcomers have the stomach to ride out markets in a time of volatility.

“Mrs. Watanabe got burned this time,” said Masafumi Yamamoto, currency economist at Nikko Citigroup in Tokyo. “The question now is whether she can make a comeback.”

Indeed, online currency trading has become a phenomenon here, with a subculture of blogs, books and investing clubs for Japan’s legions of housewife-traders. The appeal, many of these women say, lies partly in the potential that online trading offered at least some financial independence for wives who still wanted to dutifully spend their days at home.

Some of the women used their own money, some used their husband’s, and some used a combination of both. But by trading, they challenged deeply held social prohibitions in Japan against money, which is often seen here as dirty, especially when earned through market speculation.

“There are strict taboos against money that isn’t earned with sweat from the brow,” said Mayumi Torii, a 41-year-old mother of one who said she earned $150,000 since she started margin trading in currencies early last year.

Ms. Torii is one of Japan’s most famous housewife-traders. She has written a book on her investing strategies and founded a support group for home traders, the FX Beauties Club, which now has 40 members. (FX is financial shorthand for “foreign exchange.”)

But until her book was released in July, she said, she was afraid to admit even to her friends that she was trading, though her husband knew and approved. Now she is a regular guest on television programs.

Ms. Torii said she intended to keep trading, despite the recent market setbacks. She said it was her best chance to “stand on my own economically,” a necessity she discovered after her first marriage ended in divorce, and she and her son had to live off her meager savings. “I never want to feel that vulnerable again,” said Ms. Torii, now remarried.

For other women, trading offered a more modest sort of independence, giving them a chance to build up savings separate from their husbands’ accounts.