Introduction Haemoglobin is a key determinant of maximal oxygen uptake. This study's objective was to assess total haemoglobin mass (tHb-mass), as well as blood volume and morphological indices in athletes training different sports disciplines. Material and methods This study was conducted on 176 endurance and non-endurance athletes (males and females). tHb-mass, blood volume (BV), plasma volume (PV), and red cell volume (RCV) were determined by optimized carbon monoxide rebreathing method. Haemoglobin concentration (Hb), haematocrit (Hct), red blood count (RBC) were also determined. Results In endurance sports, gender regardless, no significant differences in relative mean values of tHb-mass (12.8–13.1 g/kg – males; 10.4–10.6 g/kg – females), BV (90.8–94.0 ml/kg – males; 82.7–86.9 ml/kg – females), RCV (36.6–38.0 ml/kg – males; 31.1–31.5 ml/kg – females) or of PV in males (54.2–56.4 ml/kg) were observed. The above indices’ relative values, gender regardless, were significantly lower in judo (11.2 ±0.7 g/kg, 81.8 ±5.9 ml/kg, 48.6 ±4.5 ml/kg and 33.1 ±2.0 ml/kg – males; 9.3 ±0.7 g/kg, 74.3 ±5.6 ml/kg, 46.4 ±4.0 ml/kg and 27.9 ±2.1 ml/kg – females) compared to endurance sports (p < 0.001). No substantial differences were observed in morphological blood indices in males, whereas this differentiation was found between certain sports in female athletes. Conclusions The lack of differences in tHb-mass, BV, PV and RCV in endurance sports and presence of this differentiation between various sports shows that the types of training might affect levels of mentioned indices. Measurements of tHb-mass and BV parameters prove Hb, Hct and RBC to have limited value for haematological status evaluations.