The responses of serum testosterone, sex hormone-binding globulin (SHBG) and luteinizing hormone (LH) to an oral glucose tolerance test (OGTT) were investigated in 16 healthy subjects as well as in 11 normoxaemic and 10 hypoxaemic chronic obstructive pulmonary disease (COPD) patients. The latter group were investigated on two occasions, with and without oxygen therapy. Testosterone and apparent free testosterone concentration (AFTC) fell significantly in the healthy subjects as well as in the hypoxaemic patients on oxygen therapy (p < 0.01), whereas LH increased in all groups during the OGTT (p < 0.05). There were significantly higher SHBG levels (p < 0.01), and lower AFTC levels (p < 0.05) in the hypoxaemic group compared to the healthy subjects. In the hypoxaemic group short-term oxygen therapy increased basal AFTC significantly (p < 0.05). With oxygen therapy, the 120-min glucose levels fell significantly from 9.1 +/- 3.2 to 7.6 +/- 2.7 mmol l-1 (mean +/- SD) in the hypoxaemic group (p < 0.05). In conclusion, we have found the serum testosterone and AFTC levels to decrease after an oral glucose load in healthy subjects, together with a compensatory increase in LH. The same pattern is seen in COPD patients. The hypoxaemic patients have a reduced AFTC which is partly reversed by oxygen therapy.