To investigate whether duodenal ulcer patients with painful active peptic ulcer and those with silent active ulceration have different plasma beta-endorphin levels.Forty-five patients (28 men and 17 women), aged 38-50 years, with at least a 5-year history of duodenal ulceration. Twenty-two patients had painful symptoms, while 23 had silent active duodenal ulcer.Beta-endorphin plasma levels (pmol/l) were measured during an acute episode of duodenal ulcer, before and after antisecretory therapy with omeprazole. In three patients we measured the concentration of beta-endorphin in gastric juice before and after pentagastric (6 micrograms/kg subcutaneous) stimulation.The basal values of beta-endorphin in both patients with asymptomatic and those with symptomatic duodenal ulcer showed no difference before or after 30 days of antisecretory treatment. Plasma beta-endorphin levels (median values in the normal range < 12 pmol/l) were significantly higher (Student's t-test, P < 0.005) in the asymptomatic than in symptomatic patients, both before (9.07 +/- 4.8 versus 5.6 +/- 2.5 pmol/l) and after (8.7 +/- 4.1 versus 5.7 +/- 2.4 pmol/l) omeprazole treatment. The highest levels of beta-endorphin were found in four patients with a negative history for any pain symptom (visual analogue scale score 0).Our data suggest that the opioid system, particularly beta-endorphin, is involved in the perception of pain in duodenal ulcer disease, which explains the silent clinical characteristics of some peptic ulcers. In addition, the concentration of beta-endorphin found in gastric juice indicates a possible peripheral effect of this opiate.