Peripheral nerve stimulation is the gold standard method of nerve identification in Argentina. In this article we focus on the basic principles needed to understand and perform regional blocks with the aid of a peripheral nerve stimulator, avoiding complications. Based on our experimental investigation in animals, we recommend permanently checking the equipment to always perform the blocks in an awake or slightly sedated patient and to inject the AL solution when a motor response GII is obtained with an intensity of ≤0.5 mA, a pulse duration of 100 μsec and a frequency of 2 Hz. MR at that point must disappear if intensity is decreased to 0.2 mA. Disparition of MR after local anesthetic injection is due to electrophysiologic changes of injectates and not to the physical displacement of the nerve. Paresthesia are the only protection that patients have against needle nerve contact or penetration.