An enzyme activity that catalyzes conversion of N6-(Δ2-isopentenyl)adenosine (i6Ado) to adenosine was detected in cultured tobacco tissue by Pačes et al. (1971) (Plant Physiol. 48, 775–778). Purification and characteristics of this enzyme in corn kernels have been studied. Only the naturally occurring cytokinins i6Ado and ribosylzeatin serve as substrates; the nucleoside or free base works equally as well. The reaction requires oxygen. An unstable intermediate appears to be the primary reaction product. This product decomposes to adenosine.The enzyme activity is greatest at pH 5–7. It is independent of added magnesium. The molecular weight of the enzyme is about 88 000. The activity of the enzyme in corn kernels increases from the time of pollination to about 21 days.A nucleoside hydrolase is isolated with i6Ado oxidase. The activities can be partially separated by G-150 gel filtration. The hydrolase is less stable than the i6Ado oxidase and frozen preparations lose their activity after 2 months, whereas i6Ado oxidase is stable under these conditions.