In this study canine parvovirus, CPV, was found to induce disorder in DPPC:cholesterol membranes in acidic conditions. This acidicity-induced fluidizing effect is suggested to originate from the N-terminus of the viral capsid protein VP1. In accordance with the model membrane studies, a fluidizing effect was seen also in the endosomal membranes during CPV infection implying an important functional role of the fluidization in the endocytic entry of the virus.