In 1945, Reinhold Voll discovered by accident that a medicine placed in contact with a patient's body effects the readings of an electro-dermal screening device (EDSD).

"I diagnosed one colleague as having chronic prostatitis and advised him to take a homeopathic preparation called Echinaceae 4x. He replied that he had this medication in his office and went to get it. When he returned with the bottle of Echinaceae in his hand, I tested the prostate measurement point again and made the discovery that the point reading which previously was up to 90 had decreased to 64, which was an enormous improvement of the prostate value. I had the colleague put the bottle aside and the previous measurement value returned. After holding the medication in his hand the measurement value went down to 64 again, and this pattern repeated itself as often as desired." [Voll: The Phenomenon of Medicine Testing in Electro-acupuncture According to Voll]

While checking branch points can be used to specify more refined locations of the disturbance, medicine testing serves to specify etiology and selection of medications for treatment. Medicine testing is performed on any abnormal points that are not balanced. The doctor's goal is to find one or a combination of reagents that will balance the point, i.e. cause the point tested to exhibit a "good" reading and to not have an indicator drop (a falling of the energy reading).

Reagent samples are usually sealed in glass containers. The medicine or biological compound to be tested is placed in the circuit of the EDSD (electro-dermal screening device) measurement. This can be done by placing it on an aluminum plate or container attached to the negative lead of the EDSD (electro-dermal screening device) or simply by having the patient hold the sample. All matter, including medicine, has a vibratory signal, which is distinct from all other types of matter. This signal enters the patient with the current and reacts with the signals within the patient, often changing the reading. A reagent that balances the reading will probably have a positive effect and can be considered for use as a medicine or dietary supplement. No response implies that the reagent would have no effect, and a worsening response implies a negative effect. For example, pancreas CMP readings of a person with diabetes will become balanced when the proper dose of insulin is placed within the circuit and will show a larger needle drop if refined sugar is put there. In this way medicines and dosages can be tried out without the medicine actually being ingested. This process can also be used to test for the presence of contaminants and allergies.