An electrical interferential device comprises a circuit for delivering electrical interferential energy into the body of a patient. A sensor detects a function of the autonomic nervous system of the patient and provides an output indicative of the response of the autonomic nervous system to the electrical interferential energy. A treatment regimen is selected which uses a combination of carrier and beat frequencies and electrode placement pattern that produce a desired response in the autonomic nervous system of the patient. In one embodiment of the invention, a diagnostic tool is used to determine which combination of carrier and beat frequencies are desirable and treatment is provided by a second electrical interferential device. In another embodiment of the invention, the same diagnostic tool or a portion of the same diagnostic tool may be used to treat the patient.