Synthesis of the cellular 'energy currency' ATP is catalyzed by membrane-bound F0F1-ATP synthases. The chemical reaction at three binding sites in the F1 part is coupled to proton translocation through the membrane-integrated F0 part by an internal rotation of subunits. We examined the rotary movements of the ε-subunit of the 'rotor' with respect to the b-subunits of the 'stator' by single-molecule fluorescence resonance energy transfer (FRET). Rotation of ε during ATP hydrolysis is divided into three major steps with constant FRET level corresponding to three binding sites. Different catalytic activities of the individual binding sites were observed depending on the relative orientation of the 'rotor'. Computer simulations of the FRET signals and non-equally distributed orientations of ε strongly corroborate asymmetry of catalysis in F0F1-ATP synthase.