In order to study the possible effect of acid-base alterations on growth hormone (GH) secretion in man the exercise-induced GH secretion was compared with the tentative GH release resulting from the acidosis due to hyperlactacidemia after the infusion of fructose. Submaximal exercise on bicycle ergometer resulted in a significant increase of plasma GH and lactate and in acid-base alterations. The infusion of 60 g of fructose during 60 min was without effect on plasma GH level in spite of the increase of serum lactate and slight acid-base alterations. It is concluded that no causal relationship may be found between the acid-base alterations and the increase of plasma GH during physical exercise.