Information was collected from DEA field offices and from a review of a random sample of 400 DEA investigations. Findings revealed that 85 percent of DEA's agents considered the FOIA to be inhibiting their operations. A total of 14 percent of DEA's investigations were aborted, significantly compromised, reduced in scope, or required significant amounts of additional work due to problems related to FOIA. For example, a potential informant refused to help DEA after receiving information pertaining to his own case through an FOIA request. Over one-third of DEA's agents believed that defendants had knowledge of investigative techniques used during the investigations; in almost one-fifth of the investigations, this knowledge appeared to have been gained through the FOIA. Of the 303 cases in the sample involving the use of confidential sources, almost half experienced difficulty obtaining information from witnesses or defendants, sometimes because of the FOIA. Many informants were unwillng to cooperate with DEA due to the FOIA. The problems directly attributed to the FOIA significantly increased with the sensitivity of the investigation. The study did not focus on lost opportunities for investigations, but such losses may far outweigh the adverse effects found during the research. Since prior research has revealed that over three-fifths of FOIA and Privacy Act requests originate from the criminal community, the widespread distribution of DEA reports and other materials has educated many criminals at the expense of both DEA and the general public. Figures, tables, and appendixes presenting additional data and related materials are provided. (Author summary modified)