1. Albino Wistar rats were raised in a normobaric hypoxic environment (10% O2 in N2). Two generations of hypoxic rats were observed for changes in their haemoglobin-oxygen (Hb-O2) dissociation curves (ODC), 2,3-diphosphoglycerate (2,3-DPG), haemoglobin (Hb), and Hill co-efficients at P50 (n50). The first generation were called (H1) and the second generation (H2). The control group (N) had a normoxic environment. 2. Thirty-five rats (13 N rats, 12 H1 rats and 10 H2 rats) were used. The 2,3-DPG was significantly higher in both hypoxic groups when compared with N rats (2.02 +/- 0.51 mmol/L) but 2,3-DPG of H2 rats was significantly lower than that of H1 rats (H1 = 3.48 +/- 0.58 mmol/L and H2 = 2.76 +/- 0.54 mmol/L). The haemoglobin values were N = 2.00 +/- 0.26, H1 = 2.65 +/- 0.32 and H2 = 2.36 +/- 0.30 mmol/L, respectively. 3. We observed considerable differences in Hb-O2 affinity between the three groups of rats. In standard conditions (pH = 7.400; pCO2 = 40 mmHg at 37 degrees C) the H1 rats showed a significantly decreased Hb-O2 affinity (P50,st = 37.0 +/- 1.3 mmHg) when compared with both H2 and N rats; the H2 rats showed a significantly increased Hb-O2 affinity (P50,st = 31.1 +/- 1.5 mmHg) when compared with controls N (P50,st = 34.7 +/- 2.1 mmHg). There were no significant differences in n50 values: N = 2.88 +/- 0.44; H1 = 2.88 +/- 0.77; and H2 = 2.94 +/- 0.67.(ABSTRACT TRUNCATED AT 400 WORDS)