Arterial blood from 20 healthy non-smokers (mean age 36 years) was sampled with a pre-heparinized syringe (Radiometer B129), and analysed with an automatic blood gas analyser (AVL945). Cutaneous oxygen saturation (sO2) was recorded on an ear oxymeter (Biox IIA). Mean pH +/- 2 SD was 7.392 +/- 0.072, mean arterial pCO2 +/- 2 SD was 5.15 +/- 0.90 kPa, and mean arterial pO2 +/- 2 SD was 13.68 +/- 1.90 kPa. Standard deviation for differences in pairs of analyses (SD) was, for pH 0.008, 0.20 kPa for pCO2, and 0.33 kPa for pO2. In arterial blood from 20 hypoxic patients, SD for pO2 was 0.10 kPa. Mean cutaneous sO2 +/- 2 SD was 96.7 +/- 2.2%, and mean calculated arterial sO2 +/- 2 SD was 97.6 +/- 1.0%. Mean arterial pO2 was higher than that expected from the literature.