Physical training in women was associated with a significant decrease in serum Fe levels suggesting a state of deteriorating Fe stores. To further study this phenomenon, 17 women, aged 19-23 yr, volunteered to participate in a 10 wk physical training program to study the effect of training on serum Fe levels. The training consisted of three 20-25 min exercise bouts /wk on a bicycle ergometer with individual workloads equivalent to approximately 70% of each subject''s maximum aerobic capacity. Additionally, 8 women, aged 19-28, volunteered to act as a control group. Assessments of Hb, hematocrit (Hct), serum iron (SeFe) and maximum O2 uptake (.ovrhdot.VO2 max) were made on both groups prior to and at the conclusion of the training period. Upon completion of training, .ovrhdot.VO2 max (ml/kg per min) increased by 11% (P < .05) whereas Hb and Hct showed no significant changes for the training group with respect to the control group. SeFe levels (ug/100ml) in the training group did not differ significantly from those of the control group in pre-training (128.8 .+-. 7.6 vs. 103.7 .+-. 13.7, .hivin.X .+-. SE) and post-training (126.6 .+-. 7.9 vs. 120.9 .+-. 16.3, .hivin.X .+-. SE) conditions. Neither day of menstrual cycle nor use of oral contraceptives nor use of Fe supplements had any systematic effect on SeFe levels. Short term physical training in college-age women apparently does not significantly lower SeFe levels.