The physiological responses of fruits and vegetables toransit conditions such as vibration, temperature, humidity and air composition were investigated as a basic problem of postharvest handling of horticultural crops. Temperature: The respiratorry metabolism of some fruits and vegetables was disturbed by rapid change of ambient temperature exceeding the range of 20℃. Quality deterioration of some vegetables under fluctuating temperatures was rapid compared to those held under constant temperature. These effects of temperature on the physiology and keeping quality of horticultural crops were different depending on the kind of commodity and its developmental stage. Air composition: Critical O2 concentration estimated by extinction point, the lowest O2 level at which the respiratory quotient remains at 1.0, was different for the various horticultural crops. The respiratory responses of fruits and vegetables to high CO2 were different and depended on the kind of commodity and its developmental stage. In non-climacterric fruits and several vegetables, in which ethlene evolution was not detected, high CO2 had litter or no effect at all on respiration. In some vegetables such as cucumber and lettuce treated with high CO2, ethylene evolution was induced during or after treatment and them respiration increased. These results indicate that the respiratory response of fruits and vegetables to high CO2 might be mediated through the effects of CO2 on ethlene synthesis and/ or action. Humidity: The respiratory responses of horticultural crops to relative humidity seemed to be classified into three groups; accelerative, inhibitive and insensitive at low humidity. In climacteric fruit such as bananas, ripening was accelerated under low humidity. Softening was observed in some fruits and vegetables nuder low humidity. The induction of softening seemed to be independent of endogenous ethylene concentration. These results may indicate that polygalacturonase activity is induced and then degradation of cell wall polysaccharides is initiated by water deficit stress under low humidity. Vibration: Some fruits and vegetables were physiologically sensitive to artificial vibrating conditions which were not sufficient to produce direct injury. Through intensive vibration, some metabolic pathways were suppressed while others were activated. AS a result, intensive vibration above the critical point for every fruit and vegetable caused quality deterioration. Based on the above observations, improvement of postharvest handling techniques of horticultural crops are discussed from a physiological point of view.