Cytokinin oxidase has been purified to apparent homogeneity from Zea mays kernels as indicated by a single protein staining spot on a 2-D, IEF/SDS PAGE gel. Polyclonal antibodies raised to this protein were able to precipitate cytokinin oxidase activity from a highly active, partially purified (QAE-Sephadex) preparation in the presence of fixed Staphylococcus aureus cells. The polyclonal antibodies raised to cytokinin oxidase from Z. mays crossreact with a similar protein in partially purified cytokinin oxidase preparations from dried wheat seeds.