Three modulating mechanisms of the "gate-control theory" provide a plausible explanation of how acupuncture analgesia works. In particular, the inhibitory effects of the brainstem reticular formation on the transmission of pain signals in the spinal cord or at higher ttransmission levels seems to provide a powerful explanatory concept. Intense stimulation through acupuncture needles could activate this inhibitory brainstem system, thereby closing the gate to pain signals.