Testosterone has a steeply dose-dependent effect on muscle mass and strength irrespective of gonadal status. So, for reasons of fairness, people who engage in competitive sports should not administer exogenous testosterone raising their blood testosterone levels beyond the range of normal. There is a ban on exogenous androgens for men and women in sports, but an exception has been made for men with androgen deficiency due to pituitary or testicular disease. Men who receive testosterone administration for the indication hypogonadism have an interest in the use of testosterone preparations generating blood testosterone levels within the normal range of healthy, eugonadal men. On the grounds of a positive correlation between blood testosterone concentrations muscle and volume/strength, they are best served with a parenteral testosterone preparation, rather than transdermal testosterone, but they should not run the risk of being excluded from competition because of supraphysiological testosterone levels. The latter is a realistic risk with the traditional parenteral testosterone esters. The new parenteral testosterone undecanoate preparation offers much better perspectives. Its pharmacokinetics have been investigated in detail and there is a fair degree of predictability of resulting blood testosterone levels with use of this preparation.