Cytokinin activity was found in mature black olive fruits while in green fruits the activity was markedly lower. The substances with cytokinin activity showed chromatographic properties similar to those of nucleotides. Acid hydrolysis caused a shift of the active zone in the organic phase of 1-butanol-acetic acid-water (4:1:5) from R(F) 0.1 to R(F) 0.8. The possible relation of these endogenously appearing cytokinins to anthocyanin accumulation and aging of the fruit is discussed.