N6-(Δ2-Isopentenyl)adenosine, a component of tRNA, displays biological activity in both plant and animal systems. As part of a study of the biological behavior of this nucleoside, its degradation in animal tissues has been studied. An enzyme that catalyzes conversion of this nucleoside to inosine has been partially purified from chicken bone marrow. The enzyme preparation also catalyzes conversion of adenosine to inosine at about 40 times the rate of conversion of N6-(Δ2-isopentenyl)adenosine. A series of analogues of this nucleoside has been tested as substrates. The Δ3-isomer, n-pentyl, isopentyl, and furfuryl derivatives are readily cleaved. Hydroxylated derivatives of the Δ2-isopentenyl side chain, however, do not serve as substrates. Adenosine aminohydrolase from calf intestinal mucosa also catalyzes conversion of N6-(Δ2-isopentenyl)adenosine to inosine, although in order to obtain a measurable rate, the concentration of enzyme must be about 1000 times that needed to catalyze conversion of adenosine.