Abstract A field-exposure research facility was constructed to provide a controlled environment to determine the influence of the various components of ozone exposure (concentration, frequency and duration) on plant response. The facility uses modified open-top chambers and an automated control system for continuous delivery and control of single or multiple pollutants over a growing season. Numerous exposure profiles (e.g. various episodic regimes, daily peak profiles with sinusoidal-type or square-wave type peaks) can be produced and controlled in all chambers. Ozone is produced by commercially available generators; their outputs are controlled by an HP 41CV hand-held computer through a Hewlett-Packard Interface Loop System (HP-IL). Chamber microenvironmental data and ozone concentration data are collected continuously with a data acquisition system that includes mean hourly ozone concentration, air and soil temperature, relative humidity and solar radiation. The hourly ozone concentration in each chamber ranged from 2 to 12% of the requested concentration over a 174-day season. Initial studies with this facility compared the response of alfalfa and tall fescue growth to episodic and daily peak exposure profiles with equivalent integrated exposure indices over the growing season. Over the period of three cuttings (133 days) alfalfa growth was reduced more when exposed to the episodic profile than with the exposure regime of daily ozone peaks. Tall fescue growth was reduced only slightly over a period of three cuttings (90 days) when exposed to either regime.