A lot of attention has been focused on the millions of Mexican workers who are crossing the border illegally to find work in the United States. They fill jobs many Americans prefer not to take. They also reduce the unemployment problem in Mexico, and the remittances they send back home benefit Mexico's economy.

But there is another group of émigrés Mexico does not want to see leave: hundreds of middle and upper-class families have been buying properties in cities such as Houston and San Antonio, to escape violent crime in their home country.  That has a negative impact on the Mexican economy. But their fears persist despite some significant advances in the fight against crime there.

In many Mexican border towns, the streets resemble shooting galleries, as rival drug gangs fight it out. Innocent civilians are sometimes caught in the crossfire. Here in Mexico City, the biggest threat comes from kidnapping gangs. Mexico is now second only to Colombia as the world's worst country for kidnapping.

Special Mexican police units created by President Vicente Fox have taken on organized crime and scored some successes reducing the incidence of certain types of kidnapping, assault and robbery.

But Mexican criminal justice expert Jorge Chabat says it's hardly enough.

"In terms of kidnappings, the problem is a little bit better. The problem has decreased in gravity because the federal agents who do the investigation in that area it is working pretty well, but only in preventing kidnapping,? he says. ?When they are dealing with drug trafficking, the results are pretty bad, we do not see any success there."

Mr. Chabat says the enormous profits from the illicit drug trade fuel corruption and that taking out one gang leader only opens the way for others to move in.  He says the climate of violence has a negative impact on the nation's overall economy.

"This is one of the associated costs of the insecurity. It is not only the people in the streets who pay for that, it is also the economy, the Mexican economy, that pays for that."

Part of the problem is the low regard Mexicans have for their police.  From her office at the Colegio de Mexico institute of higher learning, Professor Cecilia Toro blames society at large for police corruption.

"Society is responsible for the kind of police we have,? she told us. ?You see Mexicans go out in the street and if they commit a minor infraction, the first thing they want is to give some money to the police to get rid of him. We do not really want the police we are asking for."

Ms. Toro says police officers who try to resist corruption and really pursue drug traffickers and other dangerous criminals often find themselves without adequate support.

"To be an honest police, bring this man to the court and know that the next day he will be on the street and probably trying to get you, I would not be a police in that situation," said the professor.

She says judicial reforms must go hand-in-hand with any attempts to modernize and professionalize police forces. Ms. Toro agrees with government officials who cite progress in some areas in the fight against crime. But she says the lucrative drug trade and the battles between rival factions have created a dangerous class of killers, who will continue to be a challenge.

"For very little, for 5,000 pesos, you can find someone who is armed and willing to kill someone."

She says facing the power of the drug trafficking gangs and the criminal community they have fostered is Mexico's biggest challenge.