There are two categories of informants: the one-time informant and the informant who regularly provides information to police. A one-time informant may provide important information which must be immediately verified due to time constraints. The reliability of the information may also be crucial in determining whether to commit investigative resources, and confirmation by other means than the polygraph may jeopardize an investigation. The polygraph can be helpful in determining what the informant knows and has observed or heard. In the case of regular informants, it is important to determine their claims of access to important information, such as the claim of a close relationship with the potential subject of an investigation. The polygraph examination can also determine whether an informant correctly performed departmental instructions and has kept his/her informant status confidential. Informants may be periodically examined for security purposes. The informant should not be treated as a suspect, and the examiner must be careful not to jeopardize the relationship between the informant and the officer handling the informant. Probable-lie control question tests are the tests most widely used by Federal and police examiners, but the relevant/irrelevant test eliminates problems associated with the aforementioned test. The directed-lie control question test was developed by a Federal agency with an informant testing program for the specific purpose of testing informants. 2 footnotes.