We have used the tetrameric nature of the fluorescent protein DsRed to cross-link F(1)F(O)-ATPase complexes incorporating a subunit gamma-DsRed fusion protein in vivo. Cells expressing such a fusion protein have impaired growth relative to control cells. Strikingly, fluorescence microscopy of these cells revealed aberrant mitochondrial morphology. Electron microscopy of cell sections revealed the absence of cristae and multiple layers of unfolded inner mitochondrial membrane. Complexes recovered from detergent lysates of mitochondria were present largely as tetramers. Co-expression of 'free' DsRed targeted to the mitochondria reduced F(1)F(O)-ATPase oligomerisation and partially reversed the impaired growth and abnormal mitochondrial morphology. We conclude that the correct arrangement of F(1)F(O)-ATPase complexes within the mitochondrial inner membrane is crucial for the genesis and/or maintenance of mitochondrial cristae and morphology. Our findings further suggest that F(1)F(O)-ATPase can exist in oligomeric associations within the membrane during respiratory growth.