Ethylene production is involved in many plant physiological processes including stress responses and is frequently associated with foliar senescence. Ethylene emission is a common plant response to many biotic and abiotic stresses. We have cloned two ACC synthase cDNAs (OIP-1, PAC-1) from the leaves of ozone treated Solanum tuberosum L. plants. Plants treated with ozone produced ethylene within 1 hour following treatment initiation. Levels continued to increase reaching a peak after 2 h. PAC-1 was expressed after 1 hour reaching a maximum by 2 hours and showed a marked decline after 4 h. OIP-1 was first expressed after 2 hours and high levels of expression continued up to 4 hours following treatment initiation. Leaves treated with CuCl2 produced high levels of ethylene within 0.5 hour after treatment initiation. Ethylene levels continued to increase reaching a peak after 2 hours with no change after 4 h. PAC-1 was expressed after 0.5 hour reaching a peak at 1 hour and showed a progressive decline from 2 to 4 h. However, OIP-1 expression was first detected 2 hours following treatment initiation and high levels of expression continued up 4 h. Leaves exposed to Alternaria solani produced increased levels of ethylene 1 day following inoculation reaching a peak after 3 days. PAC-1 was expressed at a low level 1 day after inoculation and expression remained constant for the duration of the experiment, whereas, OIP-1 was not expressed until day 4.