Four cultivars field-grown Phaseolus vulgaris L., differing in their morphological characteristics, were exposed to charcoal-filtered air (CF), non-filtered air (NF), or 1.5 times greater than ambient ozone O 3 concentrations from July to September in Riverside, California (USA). The objective of the study was to determine the relative susceptibility of the four cultivars to O 3 and to relate susceptibility to O 3 to the physiological characteristics of the cultivars, particularly to rates of stomatal conductance. Compared with bean yields in CF chambers. ambient O 3 reduced yields by 65% for ‘Sutter Pink’, 73% for ‘Yolano Pink’ and 44% for ‘Sal Small White’. One cultivar, ‘Linden Red Kidney’, had increased yields in NF relative to CF treatments. The sequence of susceptibility to O 3 for both visible foliar injury and reductions in yield in the four cultivars was the same as that for the rates of stomatal conductance. The rate of maximum conductance was significantly positively correlated with both yields in CF chambers ( r = 0.77; P < 0.05) and with O 3-induced reductions in conductance ( r=0.93; P < 0.05). The results suggests that measurements of stomatal conductance in bean cultivars could be used to screen for cultivars potentially susceptible or resistant to O 3-induced yield losses in the field.