Five phenylethanoid glycosides (acteoside, isoacteoside, beta-oxoacteoside, beta-hydroxyacteoside, and salidroside) were isolated from a cell suspension culture of Olea europaea. We examined the biosynthesis of acteoside in olive cell cultures by using feeding experiments with stable isotope labeled precursors. The hydroxytyrosol moiety of acteoside is biosynthesized from tyrosine through dopamine, whereas the caffeoyl moiety of acteoside is biosynthesized from phenylalanine via a cinnamate pathway. Dopamine is incorporated into acteoside through oxidation to the corresponding aldehyde, reduction to the alcohol, and then beta-glycosylation.