In the past few months, thieves in quest of human hair have killed a beauty shop supplier in Michigan and carried out heists across America, stealing tens of thousands of dollars worth of hair.

"Whoever did it knew exactly what they wanted," said Lisa Amosu, the owner of My Trendy Place Salon in Houston, Texas, which was recently a target.

The stolen hair is typically sold on the street or on the Internet.

The most expensive type - and the one in highest demand by thieves and customers - is remy hair, which is sold with its outermost cuticle layer intact. This allows it to look more natural and to last longer without tangling.

Remy hair from India is the most popular;it usually comes from wowen who have their heads shaved as a sign of having mastered their egos.

But remy hair extensions can cost as much as $200 a package and the average person needs at least two packages. Hundreds or even thousands of dollars are spent to have the extensions attached, often by sewing.

In addition to the Houston robbery, which netted $150,000 in hair, thieves have recently taken $10,000 in hair from a San Diego shop; $85,000 from a business in Missouri City, Texas; and $10,000 from a shop inDearborn, Michigan.

Law enforcement officials are erplexed by the sudden increase in hair,thefts and the accompanying violence. "That's the first I've heard of it," said Denise Ballew, a spokeswoman for the F.B.I.

Two years ago, thieves went after cash at the Beauty One hair supply store in Chicago; in April, they took just the hair, valued at $90,000.

Detective Vito Ferro of the Chicago Police Department ,who is investigating the April 24 robbery,said some recent hair thefts in the city appeared to be the work of people sophisticated to be the work of people sophisticated enough to have taken custom orders.

"It's like someone says, 'I'm looking for a 1992 Cadillac Eldorado,' and so you go out looking for that car," he said.

In recent weeks, packages of hair that may have sold for $100 retail have sold for as little as $25 out of car trunks around the country, the authorities said. Hair can be sold at the same types of shops that are being robbed.

"People who don't want to pay the prices will buy it from the hustle man," said Ms. Amosu.

Once ridiculed by comedians,extensions and weaves have grown in apopularity.The market for human hair, which also includes cancer patients, has seen prices rise substantially as the quality of hair and the rarity of the most popular hair have increased.

"It's sort of a sign of the times," said Neal Lester, an English professor at Arizona State University who has written on the race and gender politics of hair.

"Folks are being entrepreneurial, and weaves and hair extensions are expensive, so it's not surprising that people sell hair the way they sell things on Canal Street, like knock-off purses."

But with the increased profits has come violence.

In Dearborn, the owner of Sunrise Beauty Supply, was killed in March by gunmen who stole hair extensions worth about $10,000. Two young men have been arrested.

In Lawton,Oklahoma, the police said a hair thief fled with a store owner clinging to the hood of her car.

Salons and beauty supply shops have increased security, and some even require patrons to show identification. But heightened security did not prevent thieves in San Leandro, California, from stealing $60,000 in hair from a store in April.

"This is not O.K.," said Ann Davis, the owner of Hair Divas Distributors. "I'm a little fearful."

The New York Times