The effects of endogenous and exogenous C2H4 and C2H4 inhibitors on the postharvest leaf and flower quality of Oriental lily ‘Stargazer’ were investigated. Endogenous C2H4 was not produced by freshly harvested excised leaves or flowers. Treatment of freshly harvested excised flowers, buds, leaves, and intact cut stems with C2H4 concentrations as high as 10 µl·l−1 did not affect bud opening or longevity or the development of leaf yellowing. Therefore, treatment with anti-C2H4 compounds, such as silver thiosulfate (STS) and 1-methylcyclopropene (1-MCP), did not improve the quality of the flowers. Data thus indicate that freshly harvested ‘Stargazer’ were not sensitive to C2H4. Sensitivity of ‘Stargazer’ to C2H4, however, increased dramatically following cold storage, as exposure of cold-stored stems to C2H4 concentrations as low as 0.3 µl·l−1 significantly affected bud opening. The development of leaf yellowing on cold-stored stems was not affected by the exogenous C2H4. Pretreating cold-stored stems with 1-MCP significantly reduced blasting of small buds that failed to develop due to carbohydrate depletion and reduced the percentage of buds that did not fully open. Concurrently, 1-MCP did not affect the quality of the leaves. These data indicate that sensitivity of cut lilies to C2H4 differs following cold storage and that 1-MCP is a more suitable anti-C2H4 compound than STS. Furthermore, studies on endogenous C2H4 production revealed that, while C2H4 was not detected in freshly harvested buds and leaves, it was produced by both following cold storage. The latter produced C2H4 at a higher rate than the former. Results of this study clearly indicate that there are two situations in which lilies will benefit from pretreatment with an anti-C2H4 compound (1) when cut stems contain buds that are marginally small for opening and (2) when cut stems will be cold stored before marketing.