Temperatures have regularly been above 100 in the Rio Grande Valley since spring, and a severe drought has dried or fouled most of the remote ponds and livestock tanks where illegal immigrants sneaking across the border have found water in the past.

Yet while most of the nation's attention has focused on the big cities farther north, like Dallas, where the elderly and people without air conditioning have been dying by the dozens, the second-largest cluster of heat-related deaths has been occurring along the 2,000-mile border with Mexico.Too many of those people crossing the border illegally are carrying too little water, blindly fol-low-ing guides into the South Texas frying pan. U.S. border officials say that as of last weekend, at least 50 people have died of hyperthermia, or heat-related dehydration, this year in the fiery scrublands and deserts between the Gulf of Mexico and the New Mexico state line.

"These numbers should be seen as a bare minimum," said Richard Marroquin, deputy chief patrol agent for the Laredo Sector of about 175 miles between Eagle Pass and Falcon Lake. "They're just the ones we know about. We're often coming across skeletons and bodies that have been out there for who knows how long, so there are probably a lot more out there now."

The heat victims have been various ages, from teenagers to the elderly, and they have come alone and in groups.

"Sometimes, they'll leave the sick person behind and come out to the highway to find help," Mar-ro-quin said. "Sometimes they'll wait until they get to San Antonio or wherever they're going and send word back, which is usually too late. Often, a rancher will stumble across them, or they'll go to the ranch house for help. And sometimes, they'll just leave them there and go on, without a word."