Only 10 percent of the 77 billion pounds of toxic wastes that American industries generate are disposed of properly, according to an estimate by the Environmental Protection Agency (EPA). Illegal disposers, who can make thousands of dollars on a single truckload of wastes, use such methods as parking a tank truck full of chemicals on a back road and opening the release valve or mixing liquid wastes with construction debris or regular garbage. Although the Resource Conservation and Recovery Act requires that wastes be dumped only at regulated sites, Federal and State resources for enforcing these regulations are limited. The article describes the work of such agencies as the New Jersey Interagency Hazardous Waste Task Force, the New York State Mid-Hudson Hazardous Waste Enforcement Demonstration Project, and the Louisiana State Police to combat illegal waste disposal. Some investigators build cases using informants who work in factories or drive disposal trucks, while other investigators work undercover. Law enforcement problems include lack of staff and proper equipment for chemical analysis,problems of establishing evidence of illegal waste disposal. Photographs are given.