The responses of ‘Hamlin’ oranges to varying levels of oxygen and ethylene were studied in a series of tests during the fall of 1967. Increasing ethylene levels up to 5 to 10 ppm resulted in rapid losses of chlorophyll. With 2 days’ degreening, the optimum ethylene level appeared to be higher than during a 1-day period. High oxygen (50%) alone increased the rate of degreening, but high oxygen plus ethylene did not produce any additive degreening response over ethylene alone. Low oxygen (10%) reduced the degreening response to ethylene in both ‘Hamlin’ and ‘Washington’ Navel oranges. In a test on ‘Dancy’ tangerines, the rate of degreening was slower at 70° than at 85°F. Degreening frequently continued after removal from the degreening atmospheres, resulting in modification or elimination of original treatment differences.