The purpose of this study was to investigate the time-dependent effects of long-term prolonged exercise training on vascular volumes and hematological status. Training using seven untrained males [age 21.1 +/- 1.4 (SE) yr] initially consisted of cycling at 68% of peak aerobic power (VO2peak) for 2 h/day, 4-5 days/wk, for 11 wk. Absolute training intensity was increased every 3 wk. Red cell mass (RCM), obtained using 51Cr, was unchanged (P > 0.05) with training (2,142 +/- 95, 2,168 +/- 86, 2,003 +/- 112, and 2,080 +/- 116 ml at 0, 3, 6, and 11 wk, respectively) as were serum erythropoietin levels (17.1 +/- 4.3, 13.9 +/- 3.5, and 17.0 +/- 2.0 U/l at 0, 6, and 11 wk, respectively). Plasma volume measured with 125I-labeled albumin and total blood volume (TBV) were also not significantly altered. The increase in mean cell volume that occurred with training (89.7 +/- 0.95 vs. 91.0 +/- 1.0 fl, 0 vs. 6 wk, P < 0.05) was not accompanied by changes in either mean cell hemoglobin or mean cell hemoglobin concentration. Serum ferritin was reduced 73% with training (67.4 +/- 13 to 17.9 +/- 1 microgram/l, 0 vs. 11 wk, P < 0.05). Total hemoglobin (HbTot) calculated as the product of hemoglobin concentration and TBV was unaltered (P > 0.05) at both 6 and 11 wk of training. The 15% increase in VO2peak (3.39 +/- 0.16 to 3.87 +/- 0.14 l/min, 0 vs. 11 wk, P < 0.05) with training occurred despite a failure of training to change TBV, RCM, or HbTot.