Purpose We investigated association of hematological variables with specific fitness performance in elite team-sport players. Methods Hemoglobin mass (Hb mass) was measured in 25 elite field hockey players using the optimized (2 min) CO-rebreathing method. Hemoglobin concentration ([Hb]), hematocrit and mean corpuscular hemoglobin concentration (MCHC) were analyzed in venous blood. Fitness performance evaluation included a repeated-sprint ability (RSA) test (8 x 20 m sprints, 20 s of rest) and the Yo-Yo intermittent recovery level 2 (YYIR2). Results Hb mass was largely correlated (r = 0.62, P<0.01) with YYIR2 total distance covered (YYIR2 TD) but not with any RSA-derived parameters (r ranging from-0.06 to-0.32; all P>0.05). [Hb] and MCHC displayed moderate correlations with both YYIR2 TD (r = 0.44 and 0.41; both P<0.01) and RSA sprint decrement score (r =-0.41 and-0.44; both P<0.05). YYIR2 TD correlated with RSA best and total sprint times (r =-0.46, P<0.05 and-0.60, P<0.01; respectively), but not with RSA sprint decrement score (r =-0.19, P>0.05). Conclusion Hb mass is positively correlated with specific aerobic fitness, but not with RSA, in elite team-sport players. Additionally, the negative relationships between YYIR2 and RSA tests performance imply that different hematological mechanisms may be at play. Overall, these results indicate that these two fitness tests should not be used interchangeably as they reflect different hematological mechanisms.