The sensitivity of chrysanthemum (Dendranthema grandiflora Kitamura) 'Shuho-no-chikara' to ethylene, which causes postharvest leaf yellowing (senescence), was examined. A 24-hr exposure to 1000 ppm ethylene on day 1 or 3 after harvest did not induce leaf yellowing throughout 20-day postharvest period, although the same treatment on day 4 or 6 did. Exposure as low as 1 ppm for 24 hr to ethylene on day 10 induced leaf yellowing. When cut flowers were exposed to ethylene on day 5, the effect depended on the duration of exposure and concentration; a 12- or 24-hr exposure at 1 ppm did not induce leaf yellowing,whereas a 48-hr exposure or a 24-hr exposure at 1000 ppm did. With potted flowering plants, exposure to 1000 ppm ethylene for 24 hr on day 1, 5 or 10 did not induce yellowing of leaves under the same postharvest-environmental conditions as cut flowers. These results indicate that exogenous ethylene promotes leaf yellowing in cut 'Shuho-no-chikara' chrysanthemums and that sensitivity of leaves to ethylene gradually increases with time. In continuously ethylene-treated and untreated leaves of cut vegetative shoots, ethylene production rate peaked 3 and 5 days after harvest, respectively, and then declined. The respiration rate was slightly higher in ethylene-treated leaves. The level of 1 aminocyclopropane-1-carboxylic acid (ACC) content began to increase several days after harvest. The level was higher in continuously ethylene-treated leaves. The relationship between these parameters and the sensitivity to ethylene are discussed.