We studied the effect of nitrous oxide (N2O) diffusion on size 2 LMA cuff inflation in 52 children, 38+/-21 months of age. LMA cuffs were inflated with air (Group A) or 65% N2O, oxygen and halothane (Group B). Cuffs were inflated in a stepwise manner, achieving a cuff leak pressure of 17+/-4 cm H2O for all patients. Cuff volume and intracuff pressure increased in Group A (8.5+/-1.0 mi to 10.8+/-1.4 mi and 101+/-36 mmHg to 152+/-42 mmHg, respectively) and decreased in Group B (8.9+/-1.0 mi to 6.6+/-1.5 mi and 90+/-30 mmHg to 53+/-37 mmHg, respectively). Cuff leak pressure did not change significantly in either group. We conclude that cuff inflation with a mixture of N2O/oxygen prevents N2O diffusion into the cuff, avoiding cuff overinflation without compromising LMA function.