AbstractKinetin has been shown to act synergistically with indole‐3‐acetic acid (IAA) or calcium ion (Ca2+) to stimulate ethylene production. Several commercially available cytokinins (kinetin, kinetin‐riboside, benzyladenine, benzyladenine‐riboside, isopentenyladenine, isopentenyladenine‐riboside, and zeatin) as well as noncytokinin bases (adenine and xanthine) were administered to mung bean (Phaseolus aureusRoxb.) hypocotyls to study their effects, alone or in combination with IAA or Ca2+, on ethylene production. In the presence of IAA or Ca2+, all cytokinins tested synergistically stimulated ethylene production and were as effective or nearly as effective as kinetin. Noncytokinin bases (adenine and xanthine) were, however, inactive in th