Adenosine 3′,5′-cyclic monophosphate (cAMP) and N 6, O 2′-dibutyryl adenosine 3′,5′-cyclic monophosphate (DBcAMP) were tested for relative growth promoting activity in the soybean callus bio-assay. In contrast to cAMP, DBcAMP showed cytokinin activity. N 6-butyryladenine and DBcAMP were found to be equally active. Cytokinin activity of DBcAMP apparently does not depend on the ribosyl 3,5-cyclic monophosphate moiety of the molecule but is determined by the N 6-butyryl side chain. In a series of N 6-acyladenines (C 2–C 6) the optimum activity was obtained with a chain length of 4 carbon atoms.