The amount of water and electrolytes (primarily sodium, Na+) lost as a consequence of thermoregulatory sweating during exercise can vary considerably within and among athletes. Some factors that cause the sweat rate variability: exercise intensity, environmental conditions, heat acclimation status, aerobic capacity, genetic predisposition, body size/composition, protective equipment, sex, diet and hydration status. Sweat testing can help to estimate individual sweating rates and sweat Na+ losses to guide personalized fluid and electrolyte replacement recommendations. However, it is important to note that if sweat testing is not done correctly and in a consistent manner, sweat testing results may vary and will be inaccurate. Based on study findings to date, as well as some practical considerations, current best practices in sweat testing in the field (including collection, storage, analysis and interpretation) are proposed.