Inhibition of ethylene action by 1-MCP in climacteric tree fruit including apple and pear has confirmed a number of ripening and senescence processes are regulated by ethylene.� For apple, respiration and acid loss, softening, volatile production, and chlorophyll metabolism are slowed in the absence of ethylene action resulting in delayed ripening and a greatly extended marketing period.� While similar responses are inducible with 1-MCP in pears, a lack of predictability as to when the capacity to ripen is regained currently limits wide scale commercialization.� Inhibition of ethylene action via postharvest 1-MCP exposure can also prevent development of a number of physiological disorders including superficial scald, soft scald, and senescent core flush, however, other disorders including peel and cortex CO₂ injury can be exacerbated following 1-MCP exposure.� The physiological mechanisms by which some of these disorders proceed are poorly understood and remain to be elucidated.� Recent availability of a 1-MCP formulation suitable for field use is allowing characterization of ethylene-dependent pre-harvest developmental processes.� Of particular interest is the role of ethylene in peel pigment metabolism including anthocyanin, xanthophyll, and carotenoid accumulation, chlorophyll degradation, fruit abscission, and pre-harvest firmness loss.� The horticultural utility of this formulation is also a subject of current research.