This investigation aimed to determine whether the physical work capacity of nonanemic athletes could be improved when plasma ferritin concentrations of below 30 ng/ml were raised at least 15 ng/ml. The experimental group consisted of 15 training athletes, each of whose plasma ferritin concentration was less than 30 ng/ml (mean and SD of 19.8 +/- 8.4 ng/ml). In a control group of 16, each was measured with a plasma ferritin concentration of more than 40 ng/ml (mean and SD of 83.3 +/- 37.6 ng/ml). All participated in submaximal and maximal tests for aerobic and anaerobic power. Following iron supplementation, plasma ferritin concentration in each experimental subject increased by at least 15 ng/ml to more than 30 ng/ml, to a new mean of 46.3 +/- 15.5 ng/ml. The performance measures were also repeated, but no significant overall effects were associated with the increased plasma ferritin concentrations. These data provide no sound evidence that physical work capacity of athletes is enhanced when plasma ferritin concentrations of around 20 ng/ml are increased by at least 15 ng/ml.