Injection-drug users are making the most of an innovative needle-disposal program in Baltimore. In July, in an experiment funded by the Centers of Disease Control and Prevention, the city installed four special mailboxes in areas with heavy drug use that are far from the city needle-exchange program. Some activists initially voiced skepticism, arguing that unlike syringe swaps, the new program offered neither prevention tools nor incentive for participation. But health officials found otherwise in focus groups with users. "We asked them, 'Would you use the needle-drops?' About 75 percent said they would," said Peter Beilenson, Baltimore health commissioner. So far, the boxes have collected hundreds of dirty needles-and a few letters. "We mailed all of them," Beilenson said.