SUMMARY ENDORPHINS AND THE SYNDROME OF STRESS ULCER In this experiment the relationship between endorphins and the stress ulcer was investigated. The effect of endorphins on gastric acidity, biliary reflux, blood histamine and gastric lesions were investigated experimentally. 58 rats were taken and divided into 5 groups. 5 mg/kg Bromsulphalein (BSP) IV was given to each art in order to deterct bile reflux to the stomach. 10 rats were taken as control group. Restraint is applied to 12 rats 4 hours at + 4°C. To other 12 rats an enkephalin analogous D-A!a2-Met5-Enkephelinamide (D-ALA2-MET5-ENK.) is given at a rate of 500 !u.g/|ig/hour. Thus, a rise in blood endorphins is achieved by applying endogenous stress to one groop and giving synthetic enkephalin to other group of rats. Another 2 groups of 12 rats received an opiate antogonist noloxone 2 mg/kg/ 2 hours before endogenous stress is applied or D-ALA2-Met3-Enk. is given. So that the effects of endorphins can be prevented. After 4 hours, the pathologic changes in the gastric mucosa were examined in all rats, blood histamine, pH and BSP in gastric juice were determined. In control group gastric pH was found 2.8 ± 0.7. In rats that received stress and D-ALA2-Met5-Enk. it slightly devreased (2.4 ± 0.4, 2.1 ± 0.4). When noloxane is given pH rose again (2.5 + 0.6, 2.4 _+_ 0.2). Only in rats that received D-Ala2-Met5-Enk. the pH differences are found to be statistichally important (P