Human peritoneal macrophages, originating from peritoneal dialysis fluid and growing in vitro, support the growth and serial propagation of hepatitis B virus (HBV). The evidence for virus growth is based on (i) the regular detection of HB core antigen in twenty-one passages of macrophages by a complement fixation test using rabbit anti-HB core serum; (ii) detection of HB core and e antigen in the twenty-first passage, using an enzyme-linked immunosorbent asay; (iii) the detection of HB antigen in cultured macrophages in the fourteenth passage by an indirect immunofluorescence test using human convalescent serum; and (iv) detection of HB core antigen in the twenty-second passage by immunofluorescence test using rabbit anti-HB core serum. No CPE was observed throught twenty-one passages. It is believed that this is the first successful cultivation and serial propagation of HBV in a cell culture system in vitro. Practical aspects of this finding are discussed.