We examined 58 patients (38 men, 20 women; mean age: 45 ± 12 years; body mass index: 24 ± 4 kg/m2) with a glomerular filtration rate (GFR) ranging from 3 to 32 ml/min, in order to determine the effects of a progressive decline in renal function on total hemoglobin (THb) and exercise capacity. The THb ranged from 185 to 759 g and the hemoglobin concentration ranged from 66 to 151 g/l. Maximal exercise capacity ranged from 50 to 260 W (40-143% of the expected norm). Nearly all the patients interrupted their exercise tests due to general fatigue, leg tiredness or a combination of these factors. There was a sigificant partial correlation between THb and GFR after sex and age had been accounted for (r = 0.39; p