Abstract: The effects of O₃ and HF on ethylene release by some trees and shrubs are investigated. Some preliminary conclusions are as follows:1) When trees and shrubs were exposed to O₃ concentration higher than 0.25ppm, the ethylene release from plants of all species studied had increased remarkably before visible symptoms of injury appeared. Moreover, this production increased with increasing O₃ concentration. As plants were injured severely, ethylene release were decreased.2) The ethylene release in trees injured by HF increased remarkably.3) There was a close correlation between the abnormal abscission of leaf blades and the stress ethylene release or wound ethylene release Besides aerial pollution, the drought injury was the important factor causing the abnormal abscission of tree leaves, too.