SummaryThe study of hormonal alterations due to exercise is of growing interest because of the implications for adaptation, performance, and health. The influence of the sympathoadrenal response on energy metabolism and fluid and electrolyte balance has been of primary interest in past research. Interpretation of results, however, is difficult because of the numerous factors which need to be controlled. Limitations in the interpretation of hormone levels exist because of changes in plasma volume and/or clearance rate and the influences of timing and method of blood sampling. Other factors which must be considered are the design of exercise protocols, and various subject characteristics (sex, age, fitness level, training history, diet, emotional status, diurnal and menstrual variations). Hormonal alterations during acute exercise occur primarily because of sympathoadrenal secretion of the catecholamines which initiate mobilisation of glucose and free fatty acids. This response, in turn, stimulates other endocrine glands and cells (anterior and posterior pituitary, adrenal cortex, thyroid, parathyroid, liver, pancreas, kidney) to secrete secondary hormones which potentiate fuel mobilisation and regulate water and electrolyte concentrations. As duration of exercise increases, nutrient and ion concentrations also influence hormonal responses. In recent years, research has focused on the effect of exercise-induced hormonal alterations on reproductive functioning and various endocrine-related diseases (hypopituitarism, diabetes, osteoporosis, cardiovascular disease). These topics, as well as a better understanding of mechanisms of action via receptor activity, influences on training adaptations, and implications (if any) of hormonal alterations for the growth and development of children, provide challenges for future research.