Particles with the appearance of a virus were detected by electron microscopy in the serum of individuals with Au. These were subsequently shown to be the surface antigen particles, different from the whole virus particles. Blumberg's discovery of the Australia antigen in 1965 may technically be considered the discovery of the hepatitis B virus, but at the time of that discovery its connection with a virus was speculative. 

Purification of the Australia antigen and investigation of its physical properties. (Order of authorship in the original publication: Millman, Loeb, Bayer, Blumberg.)

Blumberg shared the 1976 Nobel Prize in Physiology or Medicine with D. Carleton Gajdusek "for their discoveries concerning new mechanisms for the origin and dissemination of infectious diseases." See also Nos. 3666.4, 6840, 6841.