OBJECTIVE: To assess stress hormone response in traumatised patients studied at the site of injury and on their way to hospital. METHODS: The study was prospective. Blood samples were taken from 77 patients immediately after the arrival of the emergency physician at the site of the accident (t1) and shortly before patients' admission to hospital (t2). Plasma concentrations of beta endorphin, cortisol, adrenocorticotrophic hormone (ACTH), prolactin, and growth hormone were measured. RESULTS: Trauma in out-of-hospital patients resulted in remarkably increased concentration of growth hormone within minutes. ACTH, cortisol, and prolactin were only moderately increased. No significant correlations were found between hormone levels and blood pressure or heart rate. The plasma ACTH concentration was significantly lower before admission to hospital than immediately after the accident. Plasma cortisol, prolactin, and growth hormone concentrations were not significantly different between the two points of observation. In samples taken immediately after the accident (t1), there was a positive correlation between both beta endorphin and prolactin and the injury severity score, whereas cortisol levels were negatively correlated with injury severity score, suggesting impaired cortisol release from the adrenal cortex after severe injury. At t1 ACTH was correlated with cortisol and beta endorphin. Patients with head injuries had hormone concentrations similar to those without head injuries but with a similar injury severity score from injuries in other parts of the body. CONCLUSIONS: Lower cortisol concentrations in the very severely injured might be due to failure of the adrenal cortex to respond normally to ACTH stimulation. Growth hormone seems to play a major role in the response to trauma, reflecting an immediate stress response.