BACKGROUND: Neuroendocrine activation is a pathophysiological response and an important prognostic marker in patients with chronic heart failure (CHF). Although chronic activation is well described, data on the responsiveness of the hormone systems are more limited. Most previous studies have looked at activation during maximal exercise, whereas we believe that activation at a submaximal level might be more pathophysiologically relevant. AIM: To compare exercise-induced neurohormonal activation between CHF patients and normal subjects using the same relative and submaximal workload. Subjects: Twenty-three newly-diagnosed CHF patients and 18 age- and gender-matched healthy subjects were exercised at two workloads, which were calculated to correspond to 50 and 75% of each individual's heart rate response. RESULTS: In CHF patients, baseline levels of ANP, BNP, AVP, PRA and ET-1 were elevated compared to healthy subjects. Exercise induced an increase in ANP, A and NA in both CHF patients and in normal subjects, however BNP was only increased in CHF patients and not in normal subjects. CONCLUSION: When CHF patients exercise at the same relative and submaximal level as age-matched healthy subjects, the relative increases in ANP, A and NA were similar, however, BNP levels only increased in the CHF group.