Fifteen patients suffering from chronic epicondylitis pain who obtained alleviation of pain with vibratory stimulation were studied to investigate the possible role of endogenous opioids in the mediation of pain alleviation of vibratory stimulation. The patients' subjective pain intensity was rated using a graphic rating scale. In five patients the changes in peripheral blood flow before, during and after vibratory stimulation were also studied. After 30 min of mechanical vibratory stimulation at 100 Hz, patients were given a double-blind intravenous injection of naloxone or saline (placebo). Twelve patients did not experience reversal of pain relief from naloxone (0.4 mg). Reversal of the pain alleviation induced by vibratory stimulation was seen in two patients after i.v. injections of naloxone and in one patient after i.v. injections of naloxone or saline. When an i.m. injection of naloxone 0.01 mg/kg was administered before and during vibratory stimulation, none of the patients experienced an antagonistic effect of the pain-reducing effect of vibratory stimulation. The results suggest that the pain relief obtained with vibratory stimulation at 100 Hz is not associated with release of endogenous opioids.