Medical practitioners are licensed by the States in which they practice. In order to prescribe controlled substances lawfully, they must also be registered with the Drug Enforcement Administration. According to Federal statutes, prescriptions must be issued for a legitimate medical purpose. Three criteria must be met in order to establish a doctor-patient relationship and prescribe drugs: the patient must desire treatment for a legitimate illness or condition; the physician must make a reasonable effort to determine the patient's medical needs; and there must be a reasonable correlation between the drugs prescribed and the patient's medical needs. When abuse is suspected, law enforcement can rely on undercover and/or documentary investigations. Recording undercover visits provides the best evidence of prescription drug abuse because taped conversations can show the doctor knows that drugs being prescribed are not for legitimate purposes. Police officers should pursue a documentary investigation when there is little chance of a successful undercover operation or the undercover operation fails to produce evidence of a physician's guilt. The documentary investigation involves five steps: survey pharmacies within certain geographic boundaries to obtain prescription data; organize the data; obtain and review patient records; interview patients; and obtain expert witness reports-testimony. 3 footnotes