Evidence has accumulated that arginine‐vasopressin (AVP) may play a role in the stress response, but little attention has been paid in this hormone during stress. The present study, therefore, investigated both plasma osmolality and salivary cortisol and levels of AVP in patients undergoing a lumbar puncture procedure for evaluation of nuclear disc prolapse. It was found that the emotional stress of the procedure significantly increased plasma levels of AVP and osmolality together with an increase in salivary cortisol. Correlational data indicated a significant positive relationship between the cortisol response and the changes in plasma osmolality. Interrelationships between osmolality, stress, vasopression and glucocorticoids are discussed.