Mitogen-activated protein kinase (MAPK) cascades have been shown to be important components in abscisic acid (ABA) signal transduction pathway. In this study, a 46 kDa MAPK (p46MAPK) induced by ABA was partially purified from maize (Zea mays) by Q-Sepharose FF, Phenyl-Sepharose FF, Resource Q, Mono QTM 5/50 GL, poly-L-lysine-agarose, and Superdex 75 prep-grade columns, and was identified as ZmMAPK5 (gi|4239889) by the matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometry. Furthermore, the kinase showed optimal activity at pH 8.0, 30 degrees C, and 10 mM MgCl(2); the K(m) for myelin basic protein (MBP) substrate and ATP were 0.13 microg microl(-1) and 62 microM, respectively. MBP was the preferred substrate, of which the threonine residue was phosphorylated. Finally, the kinase was found to respond to diverse extracellular stimuli. These results enable us to further reveal the function of the ZmMAPK5 in ABA signaling.