The ethylene content of bananas (Musa sapientum L., var. Silk Fig) is constant throughout their growth and development until ripening commences, when an abrupt increase in ethylene synthesis precedes the onset of the climacteric rise in respiration. This accelerated production rate may be required to raise the internal content of ethylene to a stimulatory level, or it may be an autocatalytic response initiated when the tissue becomes sensitive to the low level of ethylene present throughout its developmental period. Following harvest, the time required to respond to a low concentration of applied ethylene decreases steadily as the fruit ages until, just prior to the onset of natural ripening, the fruit becomes able to react rapidly to a quantity of gas closely similar to what it contained throughout the preclimacteric period.