Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Intense physical training is known to be associated with increased mineral losses through sweating (during the exercise) and also through urine (after the exercise). Nowadays physical training is recognized for adapting or damaging the muscles, depending on the intensity and duration of the effort, provoking detectable metabolic alterations in blood, mainly in the content of some ions. In this study Br, Ca, Cl, K, Mg, Na and S levels were investigated in blood of Brazilian athletes that were submitted to constant physical exercise, at Laboratrio de Bioquimica do Exercicio (LABEX/UNICAMP) using Neutron Activation Analyses technique (NAA). The blood samples were collected from male amateurs and elite athletes, ranging from 18 to 36 years old. The blood samples were irradiated in the nuclear reactor (IEA-R1, 3-4.5 MW, pool type) at IPEN/So Paulo-Brazil. The concentrations data were compared with the control group (subjects of same gender and age but not involved with physical activities). These data can be useful for evaluating the performance of endurance athletes during the period of competition preparation as well as to propose new evaluation of protocols not yet reported.2973393398Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Instituto de Pesquisas Energeticas e Nucleares (IPEN)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)