Laboratory evidence of suboptimal iron status is endemic in chronically training athletes, yet the importance of low serum ferritin values to athletic performance is unclear. The purpose of this study was to monitor iron status in nine male elite swimmers during and after a 3-week training camp at 2225 m altitude. Values for hemoglobin, hematocrit, serum iron, serum transferrin, and transferrin saturation were within the normal range and remained unchanged over the 54-day monitoring period. Serum ferritin level was significantly decreased by day 13 and continued to decline over the period at altitude. Significant recovery was observed by day 35, by which the workload and altitude were reduced. Reticulocyte counts were raised above normal values by the fifth day at altitude and remained elevated for the duration of the study, indicating increased erythropoiesis. In contrast, neither ferritin levels nor reticulocyte counts were changed in six of the nine subjects after 1 month's training at 1000 m. Food histories revealed dietary iron intakes two to three times as great as the recommended dietary allowance for iron. The draw on body iron reserves observed in this study over the heavy training period at moderate altitude indicates that adequate iron stores are necessary to provide a reservoir of iron during periods of increased iron utilization or loss. Further work is required to elucidate the sources and endpoints of the observed iron flux.