Iron and iron-binding proteins play a critical role in the physiology of many human systems, including the immune system. Intense interval exercise in trained men (mean [SD] age =31.5 [4.5] yr; VO2max = 64.3 [3.8] ml.kg-1.min-1) is associated with significant modulation of iron status parameters. The concentration of red blood cells, hemoglobin, and transferrin all increased significantly immediately post-test (P < 0.01), increases which can largely be attributed to hemoconcentration. Serum iron was elevated by approximately 25% both immediately and 1 h post-test (P < 0.08). Maximum post-test serum iron values (either immediately or 1 h post-test) were significantly elevated with respect to rest (P< 0.01). Transferrin concentration was also significantly elevated at 24 h post-test (P < 0.05). Transferrin saturation was not significantly altered by this protocol (P > 0.10). Despite a trend toward elevation at 24 h post-test, ferritin concentration was not significantly different from the resting value at any sampling point. Intense interval exercise appears to be associated with significant modulation of iron status, the biological importance of which remains to be determined.