To evaluate blood donation as a cause of iron deficiency.Serum ferritin levels were determined by enzymoimmunoassay with an SRItm autoanalyser in 500 blood donors of both sexes chosen at random and in 200 suitors for blood donation, used as control group. Iron deficiency was defined by ferritin values below 15 ng/dL. Age, sex, total number of blood donations and those carried out in the last year were all correlated for the statistical analysis, performed with the SPSS/PC+ pack.The mean ferritin value in men was 86.0 ng/dL, and in women this was 27.1 ng/dL. With respect to the control group, blood donors showed increased iron deficiency, 7.4% for men and 11.8% for women. Highly significant direct correlation was found in male donors between total donations, last-year donations and age, and between total number of donations and age in female donors; highly significant inverse correlation was found between total number of donations, last-year donations and ferritin levels among the male donors, while these correlations lacked significance in the female donors. When correlating last-year donations with mean ferritin levels in women, low, although constant, ferritin values were seen, whereas a marked descent was found in men. Iron deficiency was strikingly spread among women, ranging between 21% of those with one blood donation to 46% in those with 4 donations during the last year; in men, iron deficiency was present in 14% of those with 4 or more blood donations in the last year. With respect to total number of blood donations and mean ferritin values, iron deficiency was found in 50% of the women with 8 donations and in 12.8% of men with 14 donations. Ferritin levels decrease in blood donors with aging beyond two blood donations in both sexes.1st) Iron deficiency related to blood donation is demonstrated. This deficiency is clearly seen in men after the first blood donations and is more intense in women, as their previous reserves are lower. 2nd) Ferritin is the best marker for estimating iron deposits, and enzymoimmunoassay is the technique of choice as it seems easy to perform and is automatic. 3rd) Determining ferritin levels in the first blood donation seems advisable in order to assess previous deposits and to evaluate yearly the state or iron reserves. 4th) Iron supplement is advisable during the 4 first donations in regular blood donors and in those with iron deficiency, with ferrous sulphate at a dose of 100 mg/day for 10 days.