Water-stressed and well-watered soybean (Glycine max cvs.Williams and Corsoy) plants were exposed to increasing seasonal doses of ozone (O3) using open-top field chambers and ambient air plots. Chamber O3 treatments included charcoal filtered (CF) air, non-filtered (NF) air, NF+0.03, NF+0.06 and NF+0.09 ul/liter O3. Soil water potentials measured at 25 and 45 cm averaged - 040 M Pa and -0.05 M Pa, respectively, for the plots in the water-stressed and well-watered series. Total root length/core, root length densities, and biomasses (dry weights) were determined. In both soil moisture regimes, with both cultivars, there was a linear decrease in seed yield and top dry weight as the O3 exposure dose increased.