To the Editor. —
In answer to a reader's query (237:1736, 1977) concerning the safety of electrical stimulation in neurological tests, Mr Veale of the Food and Drug Administration states, "Scrupulous attention should also be paid to grounding, if the stimulator is ac powered and has a grounded output, especially if monitoring equipment is used or the patient is grounded in some way" [my italics].The fact is that one of the conditions for successful nerve conduction velocity studies is to have an ungrounded stimulator output. If Mr Veale's directions were followed and the stimulator output were to be grounded, no measurement of nerve conduction would be possible because of an overriding artifact. The patient, on the other hand, must always be grounded to eliminate this artifact with a ground-free stimulator.I agree with Mr Veale's conclusions in all other aspects.