Patients using domiciliary nasal ventilation, or long-term oxygen, require regular assessment which could be carried out in the home. Blood gas analysis may be regarded as an essential part of the assessment. The present study investigated the effect of a 1-h time delay on the measurement of capillary blood gases. Four samples of arterialized earlobe blood were collected from 15 outpatients. One sample was analysed immediately, the other three were stored on crushed ice and analysed at intervals of 30, 45, and 60 min post-collection. In order to examine any range effect, a wide range of PaO2 values were examined. The delay, at all levels, resulted in minor changes in the measurement of PaO2, which would be unlikely to alter clinical management. The technique might be used for the reliable assessment of patients in the home.