CELL membranes are not static systems; they continually respond to the dynamics of their environment whether it be to concentration gradients, fluid pressure gradients or temperature gradients1. We feel that the dynamics of membrane response to dilation (strain) are not understood, nor have techniques been devised for such studies. In the past the method of capillary ripples2 has been developed to measure the dynamic force balance at liquid–liquid interfaces in the presence of monomolecular films. The surface force balance includes surface tension, the surface tension gradient parallel to the interface and the surface visco-elastic constants. The capillary ripple method cannot be applied directly to biological membrane models, so we have investigated normal mode vibrations in spherical membranes. The response of spherical membranes to such motion would also relate to the membrane force balance.