Previous experimental findings on the relationship between emotional stress and motivation to ingest alcohol are contradictory. To obtain information about this relationship we tested the effects on alcohol consumption in rats subjected to two types of chronic unavoidable stressors, intermittent immobilization and social isolation, which differ in their influence on the functional state of the endogenous opioid system. To characterize the nature and magnitude of the stress induced by these stressors, we measured their effects on functional parameters which have a close relationship to the regulatory influence of endogenous opioid peptides (endogenous opioid dependence, pain sensitivity, blood pressure). Our investigations have shown that chronic intermittent immobilization, which induced development of endogenous opioid dependence, presumably due to activation of endogenous opioid systems, did not produce increased alcohol consumption. On the contrary, chronic social isolation, which did not induce development of endogenous opioid dependence, was followed by a significant increase in alcohol consumption. It is concluded that not all types of stress produce increased alcohol consumption, but that the effect on the endogenous opioid system may be a decisive factor in determining whether a stressor produces increased alcohol consumption.