The mitochondrial adenosine triphosphatase of the cestode parasite,Penetrocephalus ganapatii exists as a latent form and is activated by dinitrophenol or MgCl2. Irrespective of MgCl2 or dinitrophenol concentrations, the enzyme shows optimum activity at pH 8. Effects of inhibitors on Mg2+, dinitrophenol and Mg2++dinitrophenol activated ATPase reveal that ATPase is not highly sensitive towards oligomycin and the alteration of the redox state of the respiratory chain components by rotenone, antimycin A, azide and cyanide has little effect on ATPase activity. −SH groups of the enzyme seem to play a limited role in the hydrolysis of ATP, as the enzyme is only partially sensitive top-chloromercuribenzoic acid. Generally, cations inhibit Mg2+ stimulated ATPase and activate dinitrophenol stimulated ATPase but most of the anions are inhibitory to dinitrophenol or Mg2+ stimulated ATPase.