Emission of aroma volatile compounds (AVCs) and the activity of some related enzymes were monitored during ontree maturation of ‘Mondial Gala’ apples. Volatile esters were quantitatively prominent among the AVCs identified throughout the experiment and, in most cases, their production increased noticeably during the later stages of fruit development. However, the activity of alcohol o-acyltransferase (AAT), the enzyme directly responsible for ester production, was detectable at almost constant levels throughout the experimental period, and therefore it was not in accordance with changes in the emission of volatile esters. Multivariate analysis indicated that the increase in the production of volatile esters during maturation arose mainly from the greater availability of substrates for esterification reactions, rather than from increased AAT activity. The role of some aroma-related enzyme activities in controlling the supply of precursors for ester production is discussed.