The shape of the substrate curve for duck salt gland Na,K-ATPase during ATP hydrolysis depends on incubation conditions. Under optimal conditions (pH 7.4, 37 degrees C) this curve has an intermediate plateau at 0.7-0.9 mM ATP. Both the acidification of the medium and the decrease in the incubation temperature below 20 degrees C transforms this dependence into a simple hyperbole which is characteristic of the hydrolysis of other substrates (GTP or UTP) under optimal conditions. Recently it has been suggested that the deviation from the Michaelis-Menten kinetics during Na,K-ATPase operation is due to the formation of short-living oligomers in the course of the ATP hydrolyzing cycle. The results obtained are interpreted in terms of possible effects of temperature and pH on the interprotomer interaction in the oligomeric complexes of Na,K-ATPase.