The heat pain threshold was measured with phasic and tonic stimuli under basal conditions and after naloxone administration in 10 anorectic and 10 bulimic patients as well as in 11 healthy control subjects. Under both kinds of stimulation, the basal threshold values were elevated in the bulimic patients and in some of the anorectic patients. Naloxone did not differ from placebo in its effect on the pain thresholds (phasic and tonic), suggesting that a nonopioid mechanism was responsible for the threshold elevation found in the eating disorder patients. The plasma cortisol concentration was similar in the three groups and not correlated with the basal pain thresholds in the patients. Other indicators of dieting such as beta-hydroxybutric acid and triiodothyronine also showed no correlation with the basal pain thresholds. Significant height correlations can be interpreted as weak evidence that neuropathy is the cause of the increase in the pain threshold.