Long-term exposure to waste anesthetic gas (WAG) may lead to health problems. The purpose of this study was to compare WAG concentrations resulting from 4 combinations of fresh gas flow (FGF) and vaporizer settings during a simulated intravenous induction in which the anesthetic is deepened using a volatile anesthetic delivered via mask ventilation before intubation. By using a lung model, WAG was sampled 3 times each using 4 combinations and 3 volatile anesthetics: 3% sevoflurane, 2% isoflurane, and 6% desflurane. The combinations were FGF off/vaporizer on, FGF on/vaporizer off, both on, and both off. WAG was measured using a MIRAN Ambient Air Analyzer placed at a level approximating the anesthetist's head. One-way analysis of variance with a Student-Newman-Keuls post hoc test was used to compare the concentration of WAG among the combinations of FGF/vaporizer settings for each agent. Regardless of the agent, only the FGF on/vaporizer on combination at 60 seconds resulted in a statistically greater WAG level (P < .005). The results support using 3 of the 4 combinations examined when mask ventilation with a volatile agent accompanies intravenous induction. Future studies should examine other methods of controlling WAG levels and use time-weighted averages to help address clinical significance.