Tomato (Lycopersicon esculentum Mill. ‘Fireball’), white bean (Phaseolus vulgaris L. ‘Seaway’), and tobacco (Nicotiana tabacum L. ‘Delhi 34’ and ‘White Gold’) were pretreated with herbicides at one of three rates prior to fumigation with ozone at 0, 7.5, 15, or 30 pphm (parts per hundred million) for two 1.5-hr period. The plants were harvested 5 to 7 days after ozone fumigation, dried, and weighed. The natural logarithms of the dry weight data were subjected to multiple regression analysis to test for synergistic or antagonistic interactions between ozone and the various herbicides. Synergistic phytotoxicity was definitely observed for pebulate (S-propyl butylethylthiocarbamate) and possibly for chloramben (3-amino-2,5-dichlorobenzoic acid) in combination with ozone on tobacco ‘White Gold’ and ‘Delhi 34’, respectively. For most of the other combinations (chloramben, trifluralin α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) or monolinuron (3-(p-chlorophenyl)-1-methoxy-1-methylurea) on white bean, diphenamid (N,N-dimethyl-2,2-diphenylacetamide) or trifluralin on tomato, chloramben on tobacco ‘White Gold’, and pebulate on tobacco ‘Delhi 34’) the phytotoxicity in the presence of ozone was additive and no interaction was indicated. An antagonistic interaction between ozone and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) was indicated on the two cultivars of tobacco.