Short-term exercise has been associated with increased plasma levels of atrial natriuretic factor, a potent dilating and natriuretic hormone. In this study, the effect of exercise training on atrial natriuretic factor release during short-term exercise was investigated in men without a history of cardiovascular or other major disease. A well trained group of 10 men who exercised an average of 6,618 kcal/week was compared with a minimally trained group of 9 men who exercised 1,479 kcal/week. Maximal oxygen uptake was 55.2 ml/kg per min in the well trained group and 42.5 ml/kg per min in the minimally trained group (p less than 0.05). Plasma for atrial natriuretic factor, norepinephrine and epinephrine was obtained at rest, at 4 min of exercise and at maximal exercise. Atrial natriuretic factor was lower at rest in the minimally trained than in the well trained men (23 vs. 35.9 pg/ml, p less than 0.05). At maximal exercise, atrial natriuretic factor increased 2.6 times the value at rest in minimally trained men (59.8 pg/ml, p less than 0.05 vs. rest), but did not change in well trained men (34 pg/ml). In minimally trained men at rest, at 4 min of exercise and at maximal exercise, plasma levels of atrial natriuretic factor correlated with heart rate, cardiac output, mean arterial pressure and plasma levels of norepinephrine and epinephrine; these correlations were not found in the well trained group. Thus, short-term exercise results in a significant increase in atrial natriuretic factor in minimally trained but not in well trained men.(ABSTRACT TRUNCATED AT 250 WORDS)