The neighbors introduced themselves hesitantly at first, not by name or street address but by their various ailments.

"I've got breast cancer," one woman said.

"Oh, my husband has a brain tumor," replied the woman sitting next to her.

"My son has Down syndrome," offered a man standing nearby.

"My daughter died last month from an abdominal tumor," a woman said softly. "She was only 19."

Similar introductions rippled through an auditorium in this southwest Dallas suburb one recent as more than 500 residents, some in wheelchairs and others with portable oxygen tanks hanging from their shoulders, gathered to ask a question most had only dared whisper: Is something in Midlothian's air or water making them sick?

The evidence is largely anecdotal, and few epidemiological studies have been done. But many residents say they know too many neighbors with cancer, birth defects and lung ailments for it all to be simply a coincidence.

"I know of so many funerals of women in their late thirties and early forties who died of cancer," said Alexandra Allred, 40, whose son Tommy, 5, has been hospitalized half a dozen times for acute asthma attacks. "I can't begin to tell you how many kids have asthma, bronchitis, emphysema; how many people have skin problems. I know deep down in my gut, it's got to be the pollutants being put into our air."

The signs here proudly boast that Midlothian is the "Cement Capital of Texas," a claim bolstered by the three huge cement factories whose smokestacks tower over the town. The companies have brought thousands of jobs and years of prosperity to Midlothian, a thriving bedroom community of about 12,000 whose population is growing at more than 8 percent each year.

But environmentalists say the cement plants are also responsible for some of the worst pollution in the state as their high-temperature kilns pump out millions of pounds of toxic pollutants such as arsenic, cadmium, benzene and dioxins each year.

"There's no way we know what the effect will be of these thousands of chemicals on people's health," said Jim Schermbeck, an environmental activist with a local group called Downwinders at Risk. "But what we do know is that some of these are chemicals that we've never been exposed to before."

What no one can say for certain is whether the pollution is causing unusual health problems among Midlothian's residents.

City officials strongly deny that anything is amiss, citing more than two dozen state studies over the past 10 years that failed to find any correlation between pollution from the cement plants and adverse health effects. Local officials insist that toxic emissions from the cement plants remain within the limits set by the Texas Commission on Environmental Quality.

"I wouldn't live here or raise my kids here if I felt there was an issue of safety," said Midlothian Mayor Boyce Whatley, a 20-year resident. "I think you'll find anecdotal reports of health issues in any community you live in. My grandmother is allergic to perfume. Some people are allergic to dust mites."

Only four studies by the Texas Department of State Health Services have examined suspected disease clusters and birth defects in and around Midlothian over the past decade. One found unusual levels of Down syndrome in 1992-94, but a later study found that Down syndrome was "not significantly elevated," and other types of cancer and diseases were found in the studies to be "within normal ranges."

Schermbeck, however, faults those health studies because they were based on statistics and computer models rather than actual field research and interviews.

Moreover, environmental groups allege that the "acceptable" levels of pollution permitted by state authorities are set too high to benefit industry -- a situation that they say led Ellis County, where Midlothian is located, to exceed federal Clean Air Act guidelines last year.

Despite that lack of compliance with federal air quality standards -- a situation that endangers the distribution of federal highway funds here -- TXI, the largest cement company in Midlothian, is seeking permission from state authorities to switch off pollution control devices on its largest cement kiln.

TXI officials, who declined to be interviewed for this article, have cited the high cost of operating the pollution controls in their application to state officials for relief. Environmental groups are opposing the applications before regulatory agencies and in the courts.

"What's going on with the TXI permit alone shows that it's up to citizens groups and parents to do what the state won't," said Wendi Hammond, director of the Blue Skies Alliance, another local environmental group.

Some of those concerned citizens tried another approach earlier this month: They invited Erin Brockovich, the California environmental activist made famous in a 2000 movie starring Julia Roberts, to visit Midlothian and open an investigation into the cement plants.

But if the hundreds of citizens gathered at the local community center on a recent evening to hear Brockovich were expecting quick answers, they were disappointed. Brockovich told the audience that her law firm was only beginning the process of collecting evidence to build a potential pollution liability case -- a type of case that is particularly hard to win in Texas, environmentalists say.

"Since the movie, everybody seems to think that I have all the answers," she told the crowd. "I don't have all the answers. But I would like to get some of the facts."