Zeatin (Z), zeatin riboside (ZR), isopentenyladenine (iP) and isopentenyladenosine (iPA) were tested over a range of concentrations for the production of betacyanin in the Amaranthus betacyanin bioassay. The Amaranthus betacyanin bioassay exhibited sensitivity ZR = Z>iPA ≥ iP. However, the assay was markedly less sensitive to iPA and iP than to ZR and Z and as a consequence is not an appropriate assay for the detection of iPA and iP in plant tissues.