Although it is well known that athletes have considerably larger blood volumes than untrained individuals, there is no data available describing the blood volume variability among differently trained athletes. The first aim of the study was to determine whether athletes from different disciplines are characterized by different blood volumes and secondly to what extent the blood volume can possibly limit endurance performance within a particular discipline. We investigated 94 male elite athletes subdivided into the following 6 groups: downhill skiing (DHS), swimming (S), running (R), triathlon (TA), cycling junior (CJ) and cycling professional (CP). Two groups of untrained subjects (UT) and leisure sportsmen (LS) served as controls. Total hemoglobin (tHb) and blood volume (BV) were measured by the CO-rebreathing method. In comparison to UT (mean +/- SD: tHb 11.0 +/- 1.1 g/kg, BV 78.3 +/- 7.9 ml/kg) tHb and BV were about 35 - 40 % higher in the endurance groups R, TA, CJ, and CP (e. g. in CP: tHb 15.3 +/- 1.3 g/kg, BV 107.1 +/- 7.0 ml/kg). Within the endurance groups we found no significant differences. The anaerobic discipline DHS was characterized by very low BV (87.6 +/- 3.1 ml/kg). S had an intermediate position (BV 97.4 +/- 6.1 ml/kg), probably because of the immersion effects during training in the water. VO(2)max was significantly related to tHb and BV not only in the whole group but also in all endurance disciplines. The reasons for the different BVs are an increased adaptation to training stimuli and probably also individual predisposing genetic factors.