One hundred unpremedicated fit adult patients having elective minor day-stay surgery and general anaesthesia were randomly allocated to one of two groups. During 30 s of intravenous propofol administration (2.5 mg.kg-1), study group patients (n = 50) were instructed to take three vital capacity breaths of room air, whilst control group patients (n = 50) were given no specific instructions. Pulse oximetry was continuously recorded over the next 5 min and the lowest oxygen saturation was noted. Pre-induction oxygen saturation was the same for both groups, but the lowest median oxygen saturation in the study group patients was 94% versus 88% in the control group patients (p < 0.001). Oxygen saturation returned to the pre-induction value significantly earlier in the study group patients compared with controls (97 s vs 135 s, p < 0.01). These results demonstrate that significant desaturation occurs in patients following intravenous induction of anaesthesia with propofol. This desaturation may be attenuated by asking patients to take three vital capacity breaths of room air during induction of anaesthesia.