Recent studies of stress mechanisms in hypertension have focussed on the cardiovascular and neuroendocrine reactions to challenging or threatening psychosocial stimuli. Fixed hypertension may develop in some animal models following chronic exposure to psychosocial conflict. Acute experiments in humans show that marked sympathetically-mediated cardiovascular reactions accompany the performance of challenging tasks. Responses are more accentuated in hypertensives and in people at high risk for developing the disorder. The working hypothesis to emerge is that the haemodynamic responses that accompany attempts to cope with challenging environments may promote the spiral towards sustained hypertension in susceptible individuals.