A practical and safe heating device for sampling arterialized venous blood from a hand vein was constructed and tested under experimental conditions. Blood chemistry values (pH, pCO2, pO2 and O2 saturation) were measured in nine individuals from blood sampled from an antecubital vein and a hand vein, as well as from a hand vein that had been heated in the handwarmer. Only blood sampled from the heated hand vein gave blood gas values that were consistently in the arterial range. Mean blood gas values were 38.0 +/- 2.5 mmHg, 79.8 +/- 6.8 mmHg and 95.7 +/- 0.9% for pCO2, pO2 and O2 saturation, respectively, for blood sampled from the heated hand vein. No significant difference (P greater than 0.05) was evident in blood gas values whether blood was sampled 15, 30, 45, 60, 75 or 90 min after placing the hand in the heated handwarmer. The handwarmer enables arterialized venous blood sampling after 15 min of warming and is safe to use in any experimental or clinical situation where sampling from an artery is impractical.