This review has presented data consistent with the hypothesis that HDV may be directly cytopathic or non-cytopathic depending on the stage of infection. Nevertheless, although a majority of HDV-infected patients show evidence of liver disease, healthy carriers of the virus lead to the suggestion that different healthy carriers of HDV can exist, but particularly in the absence of a florid HBV replication. These results lead to the suggestion that different strains of HDV may result in different disease outcomes. Furthermore, the role of HBV in the pathogenetic process is unlikely to be passive, and some effort should be made to examine carefully the effects of the interplay between HBV variants and HDV and the course and pathogenicity of HDV infection (see Brunetto, this volume).