There are environmental health concerns for dental health care providers chronically exposed to trace amounts of waste nitrous oxide (N2O). This study compared the effectiveness of three N2O scavenging systems, the Porter/Brown, the Accutron, and the Matrx, in actual time during use in a standardized mock dental treatment protocol that reflected clinical practice while minimizing the influence of confounding variables. At every occasion during the procedure, the Porter/Brown scavenger system left the operatory with significantly less N2O than any of the other scavengers tested. The Porter/Brown removed between 71% and 91% of the N2O compared to the control (no device).