Recent efforts have identified psychosocial and biological factors influencing the pathogenesis of chronic pain. The present study attempted to identify whether these two variables interact and, in turn, represent an underlying mechanism in the transition from acute to chronic pain. Salivary cortisol samples were collected upon waking up and 20 minutes later daily for 2 weeks from acute pain patients. Analyses revealed a direct relationship between pain severity and hypothalamic-pituitary-adrenocortical activity for temporomandibular disorder, and a negative relationship between these variables for low back pain populations. These results highlight the possible interaction between neuroendocrine and psychological factors to increase the risk for chronic pain.