The haemoglobin concentration of runners has been reported to be often below normal (1). In the present investigation the haemoglobin and iron concentrations and the haematocrit have been determined in 45 marathon runners examined before and after the 1982 Italian Marathon Championship and in 79 runners examined before and after the 1982 Firenze-Faenza race (107 km). The results obtained suggest that the training programs followed by the marathon runners (up to 260 km per week in the months preceding the race) are accompanied by a significant decrease of the haemoglobin and iron levels and of the haematocrit. Similar results have been observed in the participants to the Firenze-Faenza race. Nevertheless in these ultramarathoners the decrease of the haemoglobin and iron concentration and of the haematocrit are less marked, possibly because their training programs are less intense than those of the marathon runners. The findings obtained are in favour of the hypothesis that the degree of "sport anaemia" might be related to the amount of training of the athletes.