Hepatitis surface antigen is synthesized in recombinant yeast hosts transformed with vectors encoding hepatitis surface antigen, preferably under the control of the yeast PGK promoter and preferably in the absence of DNA encoding the surface antigen precursor. Hepatitis surface antigen is assembled by yeast into antigenic 22 nm particles even though hepatitis surface antigen bacterial transformants were not known to be capable of assembling the surface antigen into 22 nm particles.