The effects of morphine and D-Ala2 D-Leu5 enkephalin (DADLE) on intestinal motility were studied in conscious dogs with chronically implanted electrodes. In fed dogs, the normal pattern of irregular spike activity was interrupted by morphine and DADLE; both induced regular spike activity whilst DADLE also induced quiescence. Mr2266 and naloxone abolished the regular spike activity response to morphine and DADLE, but not the quiescence induced by DADLE. Mr2267 had no antagonistic action. Nalorphine methiodide induced a morphine-like response; lower doses had no agonistic action but abolished the response to morphine. The results suggest that regular spike activity induced by morphine and DADLE is a mu receptor effect, whilst the quiescence induced by DADLE may be a delta receptor effect. Morphine appears to have a peripheral site of action.