There is a large amount of evidence that proves frequencies can affect the body in a positive manner.
Please start reading here.
http://www.rife.de/electricity_frequencies_and_cancer.html
All of the studies on that page are real peer-reviewed studies. You can enter their exact titles in quotes into Google search engine, and you will find them on PubMed and other mainstream medical websites.
By far, the most telling study is this one.
http://www.ncbi.nlm.nih.gov/pubmed/19366446
It directly supports Rife's findings.
CONCLUSION: Cancer-related frequencies appear to be tumor-specific and treatment with tumor-specific frequencies is feasible, well tolerated and may have biological efficacy in patients with advanced cancer.
Please beware, however, that there are many charlatans posing as Rife therapists. There are people claiming that their therapy is based on Rife's theories, when it is not. You have to learn to decipher what is baloney and what isn't, and make sure you don't get discouraged from the real Rife theories just because a liar may have fooled you with
fake Rife methods.
I do find it important to note that electricity will always cause some harm, no matter what people claim. You do have to be careful with it. Sometimes you have to use a poison to get rid of an even bigger poison.
Either way, this is irrelevant to Rife's actual work. Remember that Rife did not use electricity - he used light (electromagnetism) to transmit his frequencies. Devices that use the name "Rife" yet use raw electricity are not technically Rife machines at all, but they do rely on the same principles - that excessive vibration causes organisms to die in the body.
Here is a very important passage, that all need to read. It is from "Cross Currents" by Dr. Robert Becker, a very famous research scientist and doctor with dozens of published studies to his name. Dr. Clark based some of her work on his writings, and mentions his name by thanking him in her Cure for All Diseases book.
He makes a point about three key ways that electricity can be harmful. I bolded the very important parts.
Page 138, Cross Currents
"First of all, electricity passing through any substance may produce heat. The amount of heat generated depends upon the resistance of the substance and the density of the current flow. For human skin, the rule of thumb is that one milliampere (1 mA) per one square centimeter is just below the level at which cell damage due to heat is produced. Currents in excess of this may not produce perceptible heating, but they may still damage cells.
Second, if the electricity is administered via electrodes made of metal, the positive electrode will give off ions of the metal itself. [Starstruck's note: This means HEAVY METAL POISONING] In many cases, such as with stainless steel electrodes, these ions will be quite toxic to cells. This toxic effect is not limited to the cells in direct contact with the electrode, because the positively charged ions will be electrically repelled by the positive field of the electrode and the driven some distance deeper into the body. [Starstruck's note: This means you are receiving positive ions whenever you touch a positive electrode. Do you know what a charlatan on this forum tells people to do? He tells them to insert a positive DC electrical generator, otherwise known as a zapper, into saltwater, and then drink it! He claims this inserts "negative" ions. Obviously he has no clue about basic principles of electricity! It does the exact opposite - it inserts positive ions into the water.]
Third, with any level of voltage, the water within the tissues will be subjected to electrolysis, a process in which the water molecules are broken apart. In biological tissues, this produces gases, such as hydrogen, that are extremely toxic to cells. The rate at which these gases are produced is proportional to the level of voltage: the higher the voltage, the greater the amount of gas. At low voltages, the circulation of blood and tissue fluids will carry the hydrogen gas away and neutralize it; however, as voltage is increased, a certain level will be reached at which gas production is greater than the ability of the circulation to carry it away. This higher voltage is called the electrolysis level, and it results in the rapid accumulation of hydrogen gas and the death of all cells at the site. In my laboratory we measured the onset of electrolysis in animal tissues using stainless-steel electrodes. We found it to occur at about 1.1 volts - a comparatively low level."
Again, you have to determine whether the benefits outweight the positives. If you take into account the many testimonials on websites like RifeForum.com and many other locations on the web, you can easily come to the conclusion that the benefits do in fact outweight any side-effects that may occur. I believe this, after my experiences with the method. I do, however, disagree with the usage of frequencies above the audio range. They cause overexcitation of the life energy in the body, and make matters much worse. Fortunately most devices claiming to be Rife today use frequencies well below 1000 Hz. If any harmonics from a square wave are created above 20,000 KHz, they are too weak either way to have any effect.
Again, all of these warnings are irrelevant if you stick directly to Rife's method. He used light, not electricity. There are plasma devices that closely mimic this same technique. Use those if you are worried about the harmful effects of electricity.
If you wish to discuss Rife's methodology and get more expert advice on the matter, I highly recommend making an account over at RifeForum.com. Many smart people there, who value the merit of the scientific method and will happily answer your questions.