The Ca2+-ATPase activity in basal bodies of Tetrahymena pyriformis was determined by cytochemical and biochemical methods. It was found that the sites of the Ca2+-ATPase activity are associated with the basal body microtubules. A method for the isolation of the basal bodies in a purified form in amounts for biochemical assay has been developed. Some properties of basal body ATPase were examined. It was established that the enzyme activity is specific for the hydrolysis of ATP and deoxy-ATP. The characteristic behaviour of the ATPase activity in response to divalent cations was assessed: the enzyme is stimulated by Ca2+ and inhibited by Mg2+. Basal body ATPase has a pH optimum of 7.5. Electrophoretic analysis of the protein composition of basal bodies revealed proteins with molecular weights of 56 and 43 kDa, corresponding to those of tubulin and actin respectively. It is suggested that the basal body ATPase may be involved in beating of the cilia, participating in the mechanochemical processes needed for motility of Tetrahymena pyriformis.