The purpose of this study was to investigate the effects of hyperventilation and breath-holding on hormonal activity and the acid-base balance in men. Three different experimental procedures were carried out with 11 trained subjects aged 24.5 years. In experiment I, all subjects performed hyperventilation for 3 min maintaining a paced ventilation of 47 l X min-1. In experiment II, they performed a threefold maximal voluntary breath-holding, separated by 1-min periods of normal breathing. Experiment III consisted of a combination of hyperventilation immediately followed by maximal voluntary breath-holding. Capillary blood samples were taken for determination of pO2, pCO2, and pH. Venous blood samples were drawn before and at the 5th and 30th min after the cessation of the applied procedure for RIA determination of human growth hormone (HGH) and cortisol. During the last 15 s of hyperventilation, pO2 increased to 89.4 +/- 16.2 mm Hg, pCO2 decreased to 19.6 +/- 1.6 mm Hg, and pH increased to 7.652 +/- 0.041. During the last 15 s of the third breath-holding, the results were pO2 = 58.0 +/- 5.1, pCO2 = 45.7 +/- 3.7, and pH = 7.367 +/- 0.053. In experiment III, the mean values were pO2 = 42.6 +/- 7.9 mmHg, pCO2 = 39.2 +/- 4.6 mmHg, and pH = 7.320 +/- 0.024. A significant hormonal response after the applied experimental procedures was found for HGH (1.5- to 5.56-fold increase) and cortisol (1.5- to 2.2-fold increase).(ABSTRACT TRUNCATED AT 250 WORDS)