An ATPase activity is associated with maize (Zea mays) annexins. It has a pH optimum of 6.0, shows Michaelis-Menten kinetics and is not stimulated by Ca2+, Mg2+, EDTA or KCl; it is not inhibited by vanadate, molybdate, nitrate or azide, but N-ethylmaleimide inhibits by approximately 30% at 1-2 mM. These properties indicate that the activity is unlike other ATPases, although it has many features in common with the myosin ATPase. Gel filtration shows that the ATPase activity is mainly associated with a 68 kDa protein that is extracted with the p33/p35 annexins and cross-reacts with antibodies to these proteins.