Accurate systems designed to expose laboratory animals to carefully controlled concentrations of gases and aerosols are an important tool in inhalation toxicology studies. These systems are necessary for determining the dose-response relationship of toxicants under a variety of exposure conditions. The objective of this project was to develop a system, employing feedback control, to expose small laboratory animals to precise concentrations of ozone. This system needed the capability of maintaining exposures at selected levels between 0.2 to 3.0 ppm over specified periods ranging between 1 and 8 h in order to evaluate health risks associated with ozone. The overall goals of this study were (1) to develop a system capable of automatically controlling the ozone exposure levels so the steady-state error remained less than 1% and (2) to optimize the system's response time. By employing a tuned control algorithm, gas monitors, data acquisition, and a custom computer software program, these two goals were realized.