Bush bean (Phaseolus vulgaris L.) plants were exposed to ozone (O3) episodes in open-top field chambers in early and late season studies at Corvallis, Oregon. Plants were grown in cultural systems that controlled plant water status. The 7-h seasonal mean O3 concentrations were 0.067 and 0.054 ppm for the early and late season experiments, respectively. At anthesis, part of the plants were subjected to a drought-stress treatment that was maintained for 14 days, after which it was relieved. Both O3 and drought-stress treatments affected physiological and biochemical processes in beans during their reproductive stages of development. Measurements of water potential, osmotic potential and relative water content revealed a mild leaf drought stress in plants grown under water deficit conditions. Drought stress increased the foliar concentrations of several nutrients (Mg, K, Fe, S, P), while O3 exposure had very little effect. At final harvest when plants had reached pod maturation, the concentrations of total soluble sugars were reduced by O3. Both O3 and drought stress significantly affected the sum of free amino acids. Of all amino acids quantified, proline showed the most remarkable increase (up to three-fold) to drought stress. Ozone exposure impaired osmoregulation to drought stress. (Copyright (c) 1991 by Gustav Fischer Verlag, Stuttgart.)