Cytokinin activity of the 4-hydroxyphenethyl alcohol (4-HPEA) isolated from the phototrophic purple bacteria Rhodospirillum rubrum was investigated in specific bioassays. A high level of 4-HPEA activity (up to 450%) compared with that for 6-benzylaminopurine was observed on amaranth cotyledons, radish leaf cuts, tobacco pith tissue callus and strawberry, cherry and kiwifruit leaf transplants. The characteristic ability of purine cytokinins to inhibit mammalian cell proliferation was shown for 4-HPEA by incorporation of methyl-3H-thymidine into M-HeLa cells. The totality of classic cytokinin properties, displayed by 4-hydroxyphenethyl alcohol, allows the classification of this compound as a non-purine cytokinin-like substance of phenolic type.