Cucumber, onion and potato plants were grown in the greenhouse. At 2 to 3 weeks from seeding they were fumigated with ozone for short periods. Observations on the development of leaf injury symptoms and of growth effects were made over a 4-week post-fumigation period. Generally, when the plants were fumigated with 100 pphm ozone for 1 hour, there were no marked responses. Fumigation at the same concentration for 4 hours resulted in a reduction in dry weight, accompanied by leaf injury symptoms. The magnitude of such effects varied with species and cultivars. Percent reduction in dry weight ranged up to 37 in cucumber, and 47 in onion. Inhibition of flowering of potato plants was accompanied by accelerated leaf senescence. Susceptibility of the species to ozone, in decreasing order, followed the sequence: onion, cucumber, potato. In each case there was at least one relatively tolerant cultivar.