A new type of propagating wave mode has been found in thin films of superfluid helium-4. Christened 'fifth sound', its discovery is reported simultaneously by two separate research groups, writing in the same issue of Physical Review Letters: by Gary A. Williams, Ralph Rosenbaum and Isadore Rudnick of the University of California at Los Angeles (42,1282; 1979); and by G.L Jelatis, LA. Roth and J.D. Maynard working at Pennsylvania State University (op. cit., 1285).