1. Haematological investigation and blood volume measurements were carried out on forty male middle-and long-distance runners and twelve non-athletes.
2. The distribution of haemoglobin concentration, packed cell volume, erythrocyte count, total iron-binding capacity, serum and erythrocyte folate and serum vitamin B12 concentrations were essentially the same in athletes and non-athletes. The mean serum iron concentration was higher in non-athletes than in athletes. There was no difference in the above measurements between athletes taking iron and/or folate and athletes not taking these supplements.
3. Blood volume and total body haemoglobin were on average 20% higher in the athletes than in the non-athletes.
4. There was no correlation between haemoglobin concentration and blood volume in athletes. The evidence of this study suggests that haemoglobin concentration and blood volume are independently controlled.
5. 2,3-Diphosphoglycerate concentration in the erythrocytes was higher in the athletes than in the non-athletes; the mean values were 15.9 and 14.2 μmol/g of haemoglobin respectively.